Passenger detection system and detection method

ABSTRACT

A passenger detection system is presented so that the master control circuit in the system instructs the passenger airbag control circuit controlling the operation of the airbag designated for the passenger seat to be in the deployable state or not-deployable state, depending on the seating conditions of a passenger sitting on the passenger seat, for example whether the passenger is an adult or a child. The passenger detection system is operated by a plurality of antenna electrodes disposed on the passenger seat; an electric field generation device for generating an electric field around an antenna electrode; a switching circuit for connecting the electric field generation device to the various antenna electrodes; an information detection circuit for detecting information related to a current flowing in a particular antenna electrode selected by the switching circuit; a master control circuit for receiving signal data output from the information detection circuit, and judging passenger seating conditions according to the signal data; and an airbag apparatus for controlling the operation of an airbag designated for the driver seat and an airbag designated for the passenger seat.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 09/395,046,filed Sep. 13, 1999, now U.S. Pat. No. 6,559,555 the contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to passenger detection systemsand methods, and relates in particular to an improved passengerdetection system that places the airbag for the passenger, in thedeployable or not-deployable state, depending on the seating conditionsof the passenger sitting in the passenger seat in an automobile.

This application is based on Japanese Patent Applications Nos. Hei10-061299, Hei 10-077870, Hei 10-077871, Hei 10-077872, Hei 10-077873,Hei 10-083797, Hei 10-083798, Hei 10-083799, Hei 10-097782, and Hei10-153270, the contents of which are incorporated herein by reference.

2. Description of the Related Art

In general, an airbag apparatus in an automobile is aimed at protectingthe driver of the vehicle from fatal injuries, in the event of acollision, and is now considered to be an essential item for automotivesafety, and in recent years, an airbag is provided for the passenger aswell as for the driver.

An example of such an airbag apparatus is shown in FIG. 96, and iscomprised by: a driver-side squib circuit comprised by a series circuitincluding safety sensor SS1, squib SQ1, and a semiconductor switchingdevice SW1 such as field effect transistor; a passenger-side squibcircuit comprised by a series circuit including a safety sensor SS2, asquib SQ2, and a semiconductor switching device SW2 such as field effecttransistor; an electronic accelerometer (impact sensor) GS; a controlcircuit CC for judging an impact force on the basis of output signalsfrom the sensor GS, and to supply signals to the gate circuits of theswitching devices SW1, SW2.

This air bag apparatus, when a collision occurs for whatever reason,safety sensor SS1, SS2 are closed responding to a relatively minoracceleration, and the squib circuits are placed in an operable state.And, when the control circuit CC judges that a collision has definitelytaken place according to the signals from the accelerometer GS, signalsare sent to the gates of switches SW1, SW2 and the switches SW1, SW2 areclosed. As a result of a current flowing in the respective squibcircuits, the driver-side and passenger-side airbags are deployedbecause of the heating in the squib SQ1, SQ2, and the occupants areprotected from the collision impact.

However, this type of airbag apparatus is designed so that the airbagsare deployed upon collision, regardless of the presence of a passengerso that, when an adult is sitting on the passenger seat, protectiveeffect against collision can be expected, but when a child is sitting onthe passenger seat, because the seated height is shorter and the headposition is lower than an adult, the effect of airbag deployment on thechild can be more damaging. Therefore, in some cases, it may bedesirable that the airbag on the passenger-side be not deployed uponcollision, when the passenger is a child.

Accordingly, in the past, an airbag apparatus such as the one shown inFIG. 97 has been proposed to address such a concern. This airbagapparatus includes a sensor SD to detect whether a passenger is seated,and the control circuit CC judges the seating condition according to thedetected signal from the sensor SD, when a collision occurs, it isdesigned so that the control circuit CC makes the airbag apparatusdeployable or not deployable. Proposed systems are based on: either tomeasure the weight of the passenger according to a weight sensor todecide if the passenger is an adult or a child; or to record an image ofthe passenger and decide between an adult or a child based on theprocessed image.

The weight method is capable of estimating substantially whether thepassenger is an adult or a child, and based on the result, the airbag isplaced either in the deployable state or not-deployable state, tosafeguard the passenger in the event of a collision. However, bodyweight is subject to individual differences, and there is a seriousconcern in basing such a critical decision solely on loading factor, andthe efficacy of such a system is in doubt.

The imaging method is able to reasonably estimate the seating conditionof the passenger and decide whether the passenger is an adult or achild, but the method is based on comparing the current image data withvarious stored patterns so that the apparatus can be complex andexpensive.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a passengerdetection system and a method for precisely detecting the sittingconditions of a passenger occupying a seat, and based on the results ofa detection process, an airbag apparatus is instructed to be in anappropriate operational state.

To achieve the objective, the present invention provides a passengerdetection system comprising: a plurality of antenna electrodes disposedseparately on a seat; an electric field generation device for generatinga weak electric field around an antenna electrode; a switching circuitfor selecting a particular antenna electrode from the plurality ofantenna electrodes and connecting to the electric field generationdevice; an information detection circuit for generating a particularelectric field around the particular antenna electrode, and obtaininginformation related to a current flowing in the particular antennaelectrode resulting from applying the particular electric field; and acontrol circuit for receiving signal data from the information detectioncircuit and judging passenger seating conditions on the seat accordingto the signal data.

Aspect 2 of the present invention provides a passenger detection systemhaving a plurality of antenna electrodes disposed separately on a seat;an electric field generation device for generating a weak electric fieldaround an antenna electrode; a switching circuit for selecting aparticular antenna electrode from the plurality of antenna electrodesand providing an electrical connection to the electric field generationdevice; an information detection circuit for generating a particularelectric field around the particular antenna electrode, and obtaininginformation related to a current flowing in the particular antennaelectrode resulting from applying the particular electric field; acontrol circuit for receiving signal data from the information detectioncircuit and judging passenger seating conditions on the seat accordingto the signal data; and an airbag apparatus for enabling to deploy, uponcollision, an airbag designated for the seat; wherein the airbagapparatus is instructed by the control circuit to be either in thedeployable state or not-deployable state according to judging datagenerated by the control circuit. Aspect 3 of the system is that theplurality of antenna electrodes are disposed on a sitting section and/orbackrest section of the seat.

Aspect 4 of the present invention provides a passenger detection methodbased on disposing generating an electric field around a particularselected from a plurality of antenna electrodes; detecting informationrelated to a current flowing in the particular antenna electroderesulting from applying the electric field; and judging passengerseating conditions according to signal data related to the information.

Aspect 5 of the present invention provides a passenger detection methodcomprising the steps of: disposing a plurality of antenna electrodesseparately on a seat; selecting a particular antenna electrode from theplurality of antenna electrodes; generating an electric field on theparticular antenna electrode; detecting information related to a currentflowing in the particular antenna electrode resulting from applying theparticular electric field; evaluating passenger seating conditionsaccording to signal data related to the information and producing ajudgment; sending the judgment to an airbag apparatus so as to place anairbag of the airbag apparatus either in the deployable state ornot-deployable state.

As disclosed above, the present passenger detection system is based on aplurality of antenna electrodes disposed on a seat, and an electricfield is generated by connecting the electric field generation devicesuccessively to each antenna electrode by means of a switching device. Acurrent, resulting from the application of the electric field, flows ineach antenna electrode depending on the passenger seating conditions.Therefore, by detecting information related to the current flowing ineach antenna electrode, passenger seating conditions such as passengerloading and whether the passenger is an adult or a child can be detectedreadily.

Also, because high frequency low voltage signals are generated from oneelectric generation device and are distributed to the plurality ofantenna electrode by the switching action of the switching device,circuit configuration is simple and the cost of the system is low.

Especially, the airbag in the airbag apparatus can be placed in adeployable or not-deployable state depending on whether the passenger isan adult or a child. For example, if a passenger is judged to be not anadult because of a low head height, the airbag is placed in thenot-deployable state. Therefore, even if a collision occurs, the airbagis not deployed thus providing an appropriate action for a childpassenger.

Aspect 6 of the present invention provides a passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on aseat; an electric field generation device for generating a weak electricfield around an antenna electrode; an amplitude control circuit formaintaining an amplitude of forward signals substantially constant; aswitching circuit for selecting a particular antenna electrode from theplurality of antenna electrodes and providing an electrical connectionto the electric field generation device; an information detectioncircuit for generating a particular electric field around the particularantenna electrode, and obtaining information related to a currentflowing in the particular antenna electrode resulting from applying theparticular electric field; and a control circuit for receiving signaldata from the information detection circuit and judging passengerseating conditions on the seat according to the signal data.

Aspect 7 of the present invention provides a passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on aseat; an electric field generation device for generating a weak electricfield around an antenna electrode; an amplitude control circuit formaintaining an amplitude of forward signals substantially constant; aswitching circuit for selecting a particular antenna electrode from theplurality of antenna electrodes and providing an electrical connectionto the electric field generation device; an information detectioncircuit for generating a particular electric field around the particularantenna electrode, and obtaining information related to a currentflowing in the particular antenna electrode resulting from applying theparticular electric field; a control circuit for receiving signal datafrom the information detection circuit and judging passenger seatingconditions on the seat according to the signal data; and an airbagapparatus for deploying, upon collision, an airbag designated for theseat; wherein the airbag apparatus is programmed by the control circuitto be either in the deployable state or not-deployable state accordingto judging data generated by the control circuit.

Aspect 8 of the present invention provides that the plurality of antennaelectrodes are disposed on the sitting section and/or the backrestsection. The invention presented in aspect 9 is a passenger detectionsystem wherein the amplitude control circuit includes, at least, anamplitude varying circuit for varying a voltage amplitude of forwardsignals and an amplitude detection circuit for detecting the voltageamplitude and controlling the voltage varying circuit so as to maintainthe voltage amplitude substantially constant, according to outputsignals from the amplitude detection circuit.

Aspect 10 of the present invention provides a passenger detection methodby selecting a particular antenna electrode, and an electric field onthe particular antenna electrode by impressing field signals, whosevoltage amplitude is controlled substantially constant; detectinginformation related to a current flowing in the particular antennaelectrode resulting from applying the particular electric field; andjudging passenger seating conditions according to signal data related tothe information.

Aspect 11 of the present invention provides a passenger detection methodby selecting a particular antenna electrode, and an electric field onthe particular antenna electrode by impressing field signals, whosevoltage amplitude is controlled substantially constant; detectinginformation related to a current flowing in the particular antennaelectrode resulting from applying the particular electric field; andjudging passenger seating conditions according to signal data related tothe information; and sending the judgment to an airbag apparatus so asto place an airbag of the airbag apparatus either in the deployablestate or not-deployable state.

According to the invention presented in aspects 6 to 11, because thevoltage amplitude of the forward signal from the selected antennaelectrode is maintained substantially constant by the amplitude controlcircuit, little fluctuation occurs in the information related to thecurrent detected by the information detection circuit so that stabledata are obtained. Therefore, without compensating for the fluctuationsin voltage amplitude, the stored data and the detected data can becompared readily, and the present detection method can offer highprecision of detection of passenger seating conditions.

Also, seat has a plurality of separate antenna electrodes, and eachantenna electrode is made to generate an electric field successively bythe switching action of the switching circuit. Based on the electricfield, a current flows successively in each antenna electrode accordingto the seating condition of the passenger. Therefore, by detectinginformation related to the current, passenger seating conditions can bedetermined accurately and readily.

Especially, the passenger airbag of the airbag apparatus is placed ineither the deployable state or not-deployable state depending on whetherthe passenger is an adult or a child. For example, if a passenger isjudged to be not an adult because of a low head height, the airbag isplaced in the not-deployable state. Therefore, even if a collisionoccurs, the airbag is not deployed to as to produce a protective actionappropriate for a child passenger.

Aspect 12 of the present invention provides a passenger detection systemcomprised by: a plurality of antenna electrodes disposed separately on aseat; an electric field generation device for generating a weak electricfield around an antenna electrode; a switching circuit for selecting aparticular antenna electrode from the plurality of antenna electrodesand providing an electrical connection to the electric field generationdevice; an information detection circuit for generating a particularelectric field around the particular antenna electrode, and obtaininginformation related to a current flowing in the particular antennaelectrode resulting from applying the particular electric field; and acontrol circuit for receiving signal data from the information detectioncircuit and judging passenger seating conditions on the seat accordingto the signal data; wherein control circuit includes: memory means forstoring initial data SDn as reference data, obtained in a referencestate including a vacant seat state by impressing an electric field oneach antenna electrode and detecting a resulting current flow in eachantenna electrode; reception means for receiving detected data ADn,obtained when starting the passenger detection system by impressing anelectric field on each antenna electrode and detecting a resultingcurrent flow in each antenna electrode; and judging means for computinga difference between the detected data ADn and the initial data SDn toproduce essentially true data DTn, where DTn=SDn−ADn, and judgingpassenger seating conditions according to the essentially true data.

Aspect 13 of the present invention provides a passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on aseat; an electric field generation device for generating a weak electricfield around an antenna electrode; a switching circuit for selecting aparticular antenna electrode from the plurality of antenna electrodesand providing an electrical connection to the electric field generationdevice; an information detection circuit for generating a particularelectric field around the particular antenna electrode, and obtaininginformation related to a current flowing in the particular antennaelectrode resulting from applying the particular electric field; acontrol circuit for receiving signal data from the information detectioncircuit and judging passenger seating conditions on the seat accordingto the signal data; an airbag apparatus having a capability to select anoperational state of an airbag designated for the seat; andcommunication means for sending judgment data, based on a judgmentderived by the control circuit, to the airbag apparatus; wherein controlcircuit includes: memory means for storing initial data SDn as referencedata, obtained in a reference state including a vacant seat state byimpressing an electric field on each antenna electrode and detecting aresulting current flow in each antenna electrode; reception means forreceiving detected data ADn, obtained when starting the passengerdetection system, by impressing an electric field on each antennaelectrode and detecting a resulting current flow in each antennaelectrode; and judging means for computing a difference between thedetected data ADn and the initial data SDn to produce essentially truedata DTn, where DTn=SDn−ADn, and judging passenger seating conditionsaccording to the essentially true data.

Aspect 14 of the present invention provides a passenger detection methodfor a passenger detection system to detect seating conditions of apassenger seated on a seat by generating an electric field successivelyin a plurality of antenna electrodes disposed on the seat, detectinginformation related to a current flow in each antenna electrode causedby respective impressed electric field and judging passenger seatingconditions according to the information, wherein the method includes thesteps of: storing initial data SDn as reference data obtained in areference state including a vacant seat state, produced by impressing anelectric field on each antenna electrode and detecting a resultingcurrent flow in each antenna electrode; receiving detected data ADn,obtained after starting the passenger detection system, by impressing anelectric field on each antenna electrode and detecting a resultingcurrent flow in each antenna electrode; computing a difference betweenthe detected data ADn and the initial data SDn to produce essentiallytrue data DTn, where DTn=SDn−ADn; and evaluating passenger seatingconditions according to the essentially true data.

Aspect 15 of the present invention provides a passenger detection methodfor a passenger detection system to detect seating condition of apassenger seated on a seat by generating an electric field around eachof a plurality of antenna electrodes disposed on the seat, detectinginformation related to a current flow in each antenna electrode causedby respective impressed electric field, judging seating conditions basedon signal data related to the information, and sending the judgment toan airbag apparatus so as to place an airbag of the airbag apparatuseither in the deployable state or not-deployable state, wherein themethod includes the steps of: initializing sensors so as to storeinitial data SDn as reference data obtained in a reference stateincluding a vacant seat state, produced by impressing an electric fieldon each antenna electrode and detecting a resulting current flow in eachantenna electrode; and after starting the passenger detection system,receiving detected data ADn, produced by successively impressing anelectric field on each antenna electrode and detecting a resultingcurrent flow in each antenna electrode; computing a difference betweenthe detected data ADn and the initial data SDn to produce essentiallytrue data DTn, where DTn=SDn−ADn; evaluating passenger seatingconditions according to the essentially true data; sending resultingevaluation data to airbag apparatus using communication means; and priorto placing the airbag apparatus in a selected operational state,performing an SRS process by exchanging evaluation data between apassenger detection circuitry and an airbag apparatus circuitry toexamine whether or not there is abnormality in communication circuitry.

According to the invention presented in aspects 12 to 15, passengerevaluation is carried out by using the initial data SDn based on thereference state which is a vacant state of the passenger seat, and thedetected signal data ADn is corrected so that the evaluation of thepassenger seating conditions is carried out according to essentiallytrue signal data DTn according to a relation DTn=SDn−ADn. Therefore,such initialization process can eliminate the effects of subtlevariations in the installation condition of the antennae and thecharacteristics of the parts used, so that the passenger detection canbe carried out reliably and precisely.

Also, signal data related to the current flowing in a selected antennaelectrode resulting from the application of electric field are obtainedfrom a difference of the initial value stored in the control storedcircuit and the detected data, and judgment on the passenger seatingconditions is made on the basis of the difference data, and the resultsare sent to the airbag apparatus through the communication device, andfurthermore, these actions are repeated, so that the control of theairbag apparatus can be performed reliably and precisely according tothe detected data of passenger seating conditions.

Especially, by arranging to communicate the passenger seating conditionsbetween the control circuit and the control circuit of the airbagapparatus, problems in the can be identified and the system performanceis improved.

Aspect 16 of the present invention provides a passenger detection systemhaving a plurality of antenna electrodes disposed separately on a seat;an electric field generation device for generating a weak electric fieldaround an antenna electrode; a switching circuit for selecting aparticular antenna electrode from the plurality of antenna electrodesand providing an electrical connection to the electric field generationdevice; an information detection circuit for generating a particularelectric field around the particular antenna electrode, and obtaininginformation related to a current flow resulting from the particularelectric field; a control circuit for receiving signal data from theinformation detection circuit and judging passenger seating conditionson the seat according to the signal data; an airbag apparatus forenabling to deploy, upon collision, an airbag designated for the seat;and communication means for sending a resulting judgment to the airbagapparatus, wherein resulting evaluation data are sent to airbagapparatus using communication means; and prior to placing the airbagapparatus either in the deployable state or not-deployable state,checking system operation by exchanging evaluation data between apassenger detection circuitry and an airbag apparatus circuitry toexamine whether or not there is abnormality in a communication circuitrybetween the passenger detection circuitry and the airbag apparatuscircuitry.

Aspect 17 of the present invention provides a passenger detection methodby: generating an electric field successively around a plurality ofantenna electrodes disposed on a seat; detecting information related toa current flowing in successive antenna electrodes; receiving signaldata regarding the information; evaluating passenger seating conditionsaccording to received signal data and producing a judgment; sending thejudgment to an airbag apparatus; and prior to placing an airbag of theairbag apparatus in a selected operational state; checking systemoperation by exchanging SRS data between a passenger detection circuitryand an airbag apparatus circuitry to examine whether or not there isabnormality in a communication circuitry between the passenger detectioncircuitry and the airbag apparatus circuitry.

Aspect 18 of the present invention provides a passenger detection methodfor a passenger detection system to detect passenger seating conditionson a seat by generating an electric field successively around aplurality of antenna electrodes disposed on a seat; detectinginformation related to a current flowing in successive antennaelectrodes; judging passenger seating conditions according to signaldata on the information; and sending a resulting judgment to an airbagapparatus so as to place an airbag designated for the seat either in thedeployable state or not-deployable state, wherein when the seat isvacant, generating an electric field successively on the plurality ofantenna electrodes; detecting information related to a current flowingin successive antenna electrode resulting from applying the electricfield; initializing sensors so as to store initial data SDn obtained, ina reference state including a vacant seat state, by generating anelectric field successively on a plurality of antenna electrodes anddetecting information related to a current flow caused by respectiveelectric field; and after starting the passenger detection system,receiving detected data ADn, produced by successively impressing anelectric field on each antenna electrode and detecting a resultingcurrent flow in each antenna electrode; computing a difference betweenthe detected data ADn and the initial data SDn to produce essentiallytrue data DTn, where DTn=SDn−ADn; evaluating passenger seatingconditions according to the true data; sending resulting evaluation datato airbag apparatus using communication means; and prior to placing theairbag apparatus in a selected operational state, performing an SRSprocess by exchanging evaluation data between a passenger detectioncircuitry and an airbag apparatus circuitry to examine whether or notthere is abnormality in a communication circuitry between the passengerdetection circuitry and the airbag apparatus circuitry.

According to the invention presented in aspects 16 to 19, signal datarelated to the current flowing in an antenna electrode resulting fromthe electric field selectively generated on the plurality of antennaelectrodes are received in the control circuit, and based on the signaldata, passenger seating conditions are judged, and the judgment is sentto the airbag apparatus through the communication device, and theselinked actions are performed repeatedly, therefore, the airbag apparatuscan be controlled appropriately according to the passenger seatingconditions.

Especially, the judgment of passenger seating conditions is exchangedbetween the control circuit and the airbag apparatus so as to check thecommunication circuit in this process, therefore, the airbag apparatuscan be controlled appropriately and control reliability is increased.

Also, the passenger evaluation process is performed according to theinitial data SDn stored in external memory which is used to correct thedetected data ADn, so that the true data can be obtained from a relationDTn=SDn−ADn, and therefore, it is possible to eliminate such effects ofsubtle variations in the installation condition of the antenna electrodeand the characteristics of the parts used, so that the passengerdetection can be carried out reliably and precisely.

Aspect 20 of the present invention provides a passenger detection systemcomprised by an antenna electrode disposed on a seat and/or a vicinityof the seat, generation means for generating an electric field aroundthe antenna electrode, detection means for detecting information relatedto a current flowing in the antenna electrode, and evaluation means forevaluating passenger seating conditions according to the information,wherein the antenna electrode is comprised by an antenna electrodesection made of an electrically conductive material, and the antennaelectrode section surrounds a planar space where there is no antennaelectrode.

Aspect 21 of the present invention provides a passenger detection systemcomprised by an antenna electrode disposed on a seat and/or a vicinityof the seat, generation means for generating an electric field aroundthe antenna electrode, detection means for detecting information relatedto a current flowing in the antenna electrode, evaluation means forevaluating passenger seating conditions according to the information,controlling means for selecting an operational state of an airbagapparatus according to the information, wherein the antenna electrode iscomprised by an antenna electrode section made of an electricallyconductive material, and the antenna electrode section surrounds aplanar space where there is no antenna electrode.

Aspect 22 of the present invention provides an antenna electrode placedon a seat and/or a vicinity of the seat constructed so as to be used ina passenger detection system to generate an electric field around theantenna electrode, detect information related to a current flowing inthe antenna electrode, and evaluate passenger seating conditionsaccording to the information, wherein the antenna electrode is comprisedby an antenna electrode section made of an electrically conductivematerial, and the antenna electrode section surrounds a planar spacewhere there is no antenna electrode.

Aspect 23 of the present invention provides a antenna electrode placedon a seat and/or a vicinity of the seat constructed so as to be used ina passenger detection system to generate an electric field around theantenna electrode, detect information related to a current flowing inthe antenna electrode, and evaluate passenger seating conditionsaccording to the information, wherein the antenna electrode is comprisedat least by an insulating base member and an antenna electrode sectionmade of an electrically conductive material, and a lead wire having anelectrical connection to the antenna electrode section, and the antennaelectrode section surrounds a planar space where there is no antennaelectrode.

Aspect 24 of the present invention provides an antenna electrode whereinthe antenna electrode section is formed into a loop shape includingspiral, or snake, comb, radiating shapes by using an electricallyconductive metal wire or strip. The invention in aspect 25 is an antennaelectrode, wherein the antenna electrode section is formed into a loopshape including spiral, or snake, comb, radiating shapes by using aprocess including screen printing, coating, spraying, vapor depositingor electroplating of an electrically conductive material. The inventionin aspect 26 is an antenna electrode, wherein the antenna electrodesection is formed into a loop shape including spiral, or snake, comb,radiating shapes by using an etching process of an electricallyconductive material including metal strip or an electrically conductivematerial prepared by vapor deposition or electroplating.

Aspect 27 of the present invention provides an antenna electrode,wherein the base member is provided with a cover member for covering theantenna electrode section so as to unitize base member with the antennaelectrode section and the cover member. The invention in aspect 28 is anantenna electrode, wherein the antenna electrode section is provideddirectly on parts constituting the seat, including seat outer coveringand cushion member. The invention in aspect 29 is an antenna electrode,wherein the antenna electrode section and the lead wire are electricallyconnected by joining means including connection terminals and pressureterminals.

According to the invention presented in aspects 20 to 29, a plurality ofantenna electrodes provided in the seat have a space bounded by theperipheries of the antenna electrode section where there is noconductive material of the antenna electrodes. Therefore, the wirematerial is reduced and the cost is lowered. Especially, when theantenna electrode section is made of an electrically conductive wovenmaterial, reduction in the material usage means lower cost.

Also, the antenna electrodes are provided with as many vacant spaces aspossible without causing problems in use, so that the cushioning of seatis not affected. Therefore, seating comfort level is maintained and iscomparable to those seats without the antenna electrodes. Particularly,when the space is in the center of the antenna electrode section, thereis hardly any effect on the performance of the antenna electrodes.

Also, the overall antenna electrode section is produced by bonding aplurality of antenna electrodes on an insulating base member, so that itis possible to secure the spacing and arrangement of the antennaelectrodes simply by positioning the base between the outer covering andthe cushion material, without having to make any adjustments in theirpositions. After installing the section, there is no problem of shiftingof the antenna electrodes. Therefore, information obtained from theperturbation current is reliable and the precision of passenger seatingevaluation is improved.

Aspect 30 of the present invention provides a passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on asitting section and/or a backrest section of a seat; an electric fieldgeneration device for generating a weak electric field around an antennaelectrode; a current detection circuit for applying the weak electricfield to a particular antenna electrode and detecting a resultingcurrent flowing in the particular antenna electrode; and a controlcircuit for evaluating passenger sitting conditions according to signaldata received from the current detection circuit; wherein all antennaelectrodes, excepting the particular antenna electrode selected forgenerating an electric field, are impressed with a direct currentpotential or earth potential.

Aspect 31 of the present invention provides a passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on asitting section and/or a backrest section of a seat; an electric fieldgeneration device for generating a weak electric field around an antennaelectrode; a switching circuit having a plurality of switching devicesfor selecting a particular electrode and connecting the electric fieldgeneration device to the particular antenna electrode; a currentdetection circuit for applying the weak electric field to the particularantenna electrode and detecting a resulting current flowing in theparticular antenna electrode; and a control circuit for evaluatingpassenger sitting conditions according to signal data received from thecurrent detection circuit; wherein all antenna electrodes, excepting theparticular antenna electrode selected for generating an electric field,are impressed with a direct current potential or earth potential.

Aspect 32 of the present invention provides a passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on asitting section and/or a backrest section of a seat; an electric fieldgeneration device for generating a weak electric field around an antennaelectrode; a current detection circuit for applying the weak electricfield to a particular antenna electrode and detecting a resultingcurrent flowing in the particular antenna electrode; and a controlcircuit for evaluating passenger sitting conditions according to signaldata received from the current detection circuit; wherein all antennaelectrodes, excepting the particular antenna electrode selected forgenerating an electric field, are impressed with a direct currentpotential or earth potential, and evaluation data from the controlcircuit are sent to an airbag apparatus so as to place an airbagdesignated for the seat in the deployable state or not-deployable state.

Aspect 33 of the present invention provides a passenger detection methodby generating a weak electric field selectively around a particularantenna electrode selected from a plurality of antenna electrodesdisposed separately on a sitting section and/or backrest section of aseat; applying a direct current potential or earth potential to allantenna electrodes excepting the particular antenna electrode; andevaluating passenger seating conditions according to signal data of aperturbation current resulting from applying the weak electric field.

Aspect 34 of the present invention provides a passenger detection methodby generating a weak electric field selectively around a particularantenna electrode selected from a plurality of antenna electrodesdisposed separately on a sitting section and/or backrest section of aseat; applying a direct current potential or earth potential to allantenna electrodes excepting the particular antenna electrode; andevaluating passenger seating conditions according to signal data of aperturbation current resulting from applying the weak electric field toproduce an evaluation result, and sending instruction data based on theevaluation result from the control circuit to an airbag apparatus so asto place an airbag designated for the seat in the deployable state ornot-deployable state.

According to the invention presented in aspects 30 to 34, a plurality ofantenna electrodes are disposed in the sitting section and/or thebackrest section separately, and weak electric fields are generatedsuccessively around each electrode and the resulting signal data relatedto the perturbation current flowing in the antenna electrodes areprocessed to carry out the passenger detection process. However, oneantenna electrode at a time is activated with ac signals while all otherantenna electrodes are impressed with a dc voltage so that parasiticinterference can be avoided. This approach is advantageous because ofthe stability of the electric field generated, and consequently, theperturbation current measurement is also stable. Therefore, by detectingthe values of such perturbation current, it is possible to detectreadily whether the seat is vacant or the passenger is an adult or achild, thereby improving the detection precision. Especially, thecircuitry allows selection of setting the airbag apparatus to be eitherin the deployable state or not-deployable state so that unwanted airbagdeployment can be prevented.

Especially, when a dc voltage from the electric power circuit is to beapplied to all the antenna electrodes that are not generating anelectric field, the same voltage can be shared with the oscillationcircuit and control circuit, thus enabling to avoid having a separatepower source for the dc voltage and the electric field generationprocess is stabilized at low cost.

Also, because a plurality of antenna electrodes can be selectivelyswitched to the oscillation circuit and a dc voltage source by theswitching action of the switching device by signals from the controlcircuit, contact to terminals a and b of the switching devices can beperformed quickly and accurately. Thus, the perturbation current flowingin a particular antenna electrode can be detected precisely by thecurrent detection circuit, and signal data regarding the perturbationcurrent are received accurately in the control circuit.

Aspect 35 of the present invention provides a passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on aseat; an electric field generation device for generating a weak electricfield around an antenna electrode; a switching circuit for selecting aparticular electrode and connecting the electric field generation deviceto the particular antenna electrode; an information detection circuitfor applying the weak electric field to the particular antenna electrodeand detecting information related to a current flowing in the particularantenna electrode resulting from applying the weak electric field; and acontrol circuit for evaluating passenger sitting conditions according tosignal data received from the information detection circuit; wherein theelectric field generation device outputs high frequency low voltagesignals having a rectangular waveform.

Aspect 36 of the present invention provides a passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on aseat; an electric field generation device for generating a weak electricfield around an antenna electrode by outputting high frequency lowvoltage signals having a rectangular waveform; a switching circuit forselecting a particular electrode and connecting the electric fieldgeneration device to the particular antenna electrode; an informationdetection circuit for applying the weak electric field to the particularantenna electrode and detecting information related to a current flowingin the particular antenna electrode resulting from applying the weakelectric field; and a control circuit for evaluating passenger sittingconditions according to signal data received from the informationdetection circuit to produce an evaluation result, and sendinginstruction data based on the evaluation result from the control circuitto an airbag apparatus so as to place an airbag designated for the seatin the deployable state or not-deployable state.

Aspect 37 of the present invention provides a passenger detectionsystem, wherein a plurality of antenna electrodes are disposed on asitting section and/or a backrest section of a seat. The invention inaspect 38 is passenger detection system, wherein electric fieldgeneration device generates high frequency low voltage signals of arectangular waveform by switching a direct current voltage maintained ata positive constant voltage at a selected frequency. The invention inaspect 39 is a passenger detection system, wherein electric fieldgeneration device generates high frequency low voltage signals of arectangular waveform by dividing a clock signal in a control circuit ata selected interval.

Aspect 40 of the present invention provides a passenger detection methodby generating a weak electric field selectively around a particularantenna electrode selected from a plurality of antenna electrodesdisposed separately on a seat; applying high frequency low voltagesignals of a rectangular waveform on the particular antenna electrode;and detecting information related to perturbation current flowing is theparticular antenna electrode; and evaluating passenger seatingconditions according to signal data related to the information.

Aspect 41 of the present invention provides a passenger detection methodby generating a weak electric field selectively around a particularantenna electrode selected from a plurality of antenna electrodesdisposed separately on a seat; applying high frequency low voltagesignals of a rectangular waveform on the particular antenna electrode;and detecting information related to a perturbation current flowing isthe particular antenna electrode; and evaluating passenger seatingconditions according to signal data related to the information toproduce an evaluation result, and sending instruction data based on theevaluation result from the control circuit to an airbag apparatus so asto place an airbag designated for the seat in the deployable state ornot-deployable state.

According to the invention presented in aspects 35 to 41, the antennaelectrodes disposed on the seat are impressed with high frequency lowvoltage (HFLV) signals of a square waveform by the electric generationdevice, therefore, the circuit is simplified by adopting the method ofswitching a direct voltage source. Therefore, not only the electricfield generation circuit but other component circuits are alsosimplified, so that the system cost is lowered.

Especially, electric field generation device may include an HFLV sourceto produce substantially rectangular waveform by switching of a positiveelectrical power source based on clock signals in the control circuit,or by dividing the clock signal in the control circuit. This furthersimplifies the control unit circuit, and system cost is further lowered.

Further, forward signals sent to the antenna electrodes aresubstantially at a constant voltage of a square waveform, therefore,data related to information obtained by the information detectioncircuit can be processed by a simple circuit, and the passenger seatingconditions can be determined even more reliably and precisely.

Aspect 42 of the present invention provides a passenger detection systemcomprising: an antenna electrode disposed on a sitting section and/or abackrest section of a seat; an electric field generation device forgenerating a weak electric field around the antenna electrode; an ac-dcconversion circuit for converting an alternating current line voltage ina forward line, related to a perturbation current flowing in the antennaelectrode resulting from the weak electric field generated around theantenna electrode produced by connecting the antenna electrode to theelectric field generation device, to a direct current voltage; and acontrol circuit for judging passenger seating conditions according toevaluation data output from the conversion circuit.

Aspect 43 of the present invention provides a passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on asitting section and/or a backrest section of a seat; an electric fieldgeneration device for generating a weak electric field around an antennaelectrode; a switching circuit for selecting a particular electrode andconnecting the electric field generation device to the particularantenna electrode; an ac-dc conversion circuit for applying the weakelectric field to the particular antenna electrode, and converting aresulting alternating current line voltage in a forward line related toa perturbation current flowing in the particular electrode to a directcurrent voltage; and a control circuit for judging passenger seatingconditions according to signal data output from the conversion circuit.

Aspect 44 of the present invention provides a passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on asitting section and/or a backrest section of a seat; an electric fieldgeneration device for generating a weak electric field around an antennaelectrode; a switching circuit for selecting a particular electrode toserve as a sending electrode and selecting a pairing electrode serving areceiving electrode, and connecting the electric field generation deviceto the particular antenna electrode; an ac-dc conversion circuit forgenerating a weak electric field between a resulting pair of antennaelectrodes, and converting a resulting alternating current line voltagein a forward line related to a perturbation current flowing in theparticular electrode to a direct current voltage; and a control circuitfor judging passenger seating conditions according to signal data outputfrom the conversion circuit.

Aspect 45 of the present invention provides a passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on asitting section and/or a backrest section of a seat; an electric fieldgeneration device for generating a weak electric field around an antennaelectrode; a switching circuit for selecting a particular electrode andconnecting the electric field generation device to the particularantenna electrode; an ac-dc conversion circuit for applying the weakelectric field to the particular antenna electrode, and converting aresulting alternating current line voltage in a forward line related toa perturbation current flowing in the particular electrode to a directcurrent voltage; and a control circuit for judging passenger seatingconditions according to signal data output from the conversion circuitto produce an evaluation result, and sending instruction data based onthe evaluation result from the control circuit to an airbag apparatus soas to place an airbag designated for the seat in the deployable state ornot-deployable state.

Aspect 46 of the present invention provides a passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on asitting section and/or a backrest section of a seat; an electric fieldgeneration device for generating a weak electric field around an antennaelectrode; a switching circuit for selecting a particular electrode andconnecting the electric field generation device to the particularantenna electrode; an ac-dc conversion circuit for applying the weakelectric field to the particular antenna electrode, and converting aresulting alternating current line voltage in a forward line related toa perturbation current flowing in the particular electrode to a directcurrent voltage; and a control circuit for judging passenger seatingconditions according to signal data output from the conversion circuit.

Aspect 47 of the present invention provides a passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on asitting section and/or a backrest section of a seat; an electric fieldgeneration device for generating a weak electric field around an antennaelectrode; a switching circuit for selecting a particular electrode andconnecting the electric field generation device to the particularantenna electrode; an ac-dc conversion circuit for applying the weakelectric field to the particular antenna electrode, and converting aresulting alternating current line voltage in a forward line related toa perturbation current flowing in the particular electrode to a directcurrent voltage; and a control circuit for judging passenger seatingconditions according to signal data output from the conversion circuitto produce an evaluation result, and sending instruction data based onthe evaluation result from the control circuit to an airbag apparatus soas to place an airbag designated for the seat in the deployable state ornot-deployable state.

Aspect 48 of the present invention provides a passenger detectionsystem, wherein an RC time constant circuit is formed by capacitancecomponents existing in a vicinity of an antenna electrode and a resistorconnected in series to a forward circuitry including an electric fieldgeneration device. The invention in aspect 49 is a passenger detectionsystem, wherein an impedance conversion circuit is provided between aforward circuitry for sending output signals from an electric fieldgeneration device and an ac-dc conversion device. The invention inaspect 50 is a passenger detection system, wherein the impedanceconversion circuit is comprised by an operational amplifier having anamplification factor of 1. The invention in aspect 51 is a passengerdetection system, wherein the control circuit is comprised, at least, bymemory means for storing threshold value related to passenger seatingconditions, means for receiving output signals from an ac-dc conversioncircuit, and a judging section for judging passenger seating conditionsby comparing threshold values with received signal data.

Aspect 52 of the present invention provides a passenger detectionsystem, wherein the electric field generation device, the ac-dcconversion circuit, and the control circuit are housed in a commonhousing to form a control unit, which is incorporated in the seat. Theinvention in aspect 53 is a passenger detection system, wherein theelectric field generation device, ac-dc conversion circuit, and thecontrol circuit are housed in a common housing to form a control unit,and those constituting elements requiring an electric power source aresupplied with power from an electric power source Vcc outputting aconstant direct current voltage.

According to the invention presented in aspects 42 to 53, a currentrelated to the stray capacitance components existing around the seatflows in the antenna electrodes, and in such a case, the waveform of theforward signals from the electric generation device is dependent on a RCtime constant of the circuitry, and the rise time of the signals isaffected and the resulting rounding effect of the rise time depends onwhether the passenger is an adult or a child. The resulting ac voltagecan be converted in the ac-dc conversion circuit to obtaindistinguishable dc signals. This signal data are received in the controlcircuit and based on the signal data related to the dc current,passenger seating conditions can be determined precisely.

Also, because of the presence of the impedance conversion circuitbetween the signal line and the ac-dc conversion circuit, the input-sidehas a high impedance and the output-side has a low impedance. Therefore,when the control circuit receives dc output signals from the ac-dcconversion circuit, current drain by the control circuit does not affectthe performance of the signal line. Therefore, passenger seatingconditions can be detected with high precision.

Also, the electric power circuit as an element in the control unitproduces a singular power source Vcc by reducing the voltage form thebattery power to a singular dc voltage so that all the elements in thecontrol unit requiring the electrical power can be served by the sameconstant voltage Vcc, therefore, the electric power circuit and thestructure of the control unit can be simplified, so that the overallunit is simplified and the system cost is lowered.

Because the control unit is housed within the same housing as othercomponents such as the electric field generation device, switchingcircuit, impedance conversion circuit, ac-dc conversion circuit; controlcircuit; power circuit, so that assembly into the seat is facilitated.Especially, an installation space is readily available near the seatframe or its vicinity, therefore, even if the size of the control unitbecomes slightly larger, it can be simply and readily accommodated nearthe frame.

Also, the passenger seating condition is judged from the output dcsignals from the ac-dc conversion circuit and analyzed by the controlcircuit in terms of a plurality of antenna electrodes, which areselected by the switching circuit. Therefore, the control circuit basesits decision on a large amount of perturbation data obtained fromdifferent antenna electrodes, thereby improving the detection capabilityand reliability of the passenger detection system even more.

Aspect 54 of the present invention provides a passenger detection systemcomprising: an antenna electrode disposed on a sitting section and/or abackrest section of a seat; an electric field generation device forgenerating a weak electric field around the antenna electrode; anantennae interface circuit including a detection circuit for detectinginformation related to a perturbation current flowing in the antennaelectrode resulting from applying a power from the electric fieldgeneration device; a correction interface circuit including a detectioncircuit for detecting information related to a perturbation currentflowing in the antenna electrode resulting from applying a power fromthe electric field generation device; and a control circuit forcorrecting signals output from the antennae interface circuit accordingto signal data output from the antennae interface circuit and thecorrection interface circuit; wherein the antennae interface circuit andthe correction interface circuit are configured similarly and theantennae interface circuit is connected to an antenna electrode and thecorrection interface circuit is not connected to an antenna electrodeand is open-circuited.

Aspect 55 of the present invention provides a passenger detection systemcomprising: an antenna electrode disposed on a sitting section and/or abackrest section of a seat; an electric field generation device forgenerating a weak electric field around an antenna electrode; anantennae interface circuit including a detection circuit for detectinginformation related to a perturbation current flowing in an antennaelectrode resulting from applying a power from the electric fieldgeneration device; a correction interface circuit including a detectioncircuit for detecting information related to a perturbation currentflowing in an antenna electrode resulting from applying a power from theelectric field generation device; a control circuit for correctingsignals output from the antennae interface circuit according to signaldata output from the antennae interface circuit and the correctioninterface circuit; and an airbag apparatus that can be placed in aspecific operational state according to judgment data generated by thecontrol circuit; wherein the antennae interface circuit and thecorrection interface circuit are configured similarly and the antennaeinterface circuit is connected to an antenna electrode and thecorrection interface circuit is not connected to an antenna electrodeand is open-circuited.

Aspect 56 of the present invention provides a passenger detectionsystem, wherein the antennae interface circuit is comprised of, atleast: an electric field generation device for generating a weakelectric field around an antenna electrode; an ac-dc conversion circuitfor connecting an antenna electrode to the electric field generationdevice to generate an electric field, and converting ac voltage relatedto a perturbation current flowing in the antenna electrode, resultingfrom applying the electric field, to dc data. The invention in aspect 57is passenger detection system, wherein an RC time constant circuit isformed by capacitance components existing in a vicinity of an antennaelectrode and a resistor connected in series to a forward circuitryincluding an electric field generation device. The invention in aspect58 is passenger detection system, wherein an impedance conversioncircuit is provided between a forward circuitry for sending outputsignals from an electric field generation device and an ac-dc conversiondevice. The invention in aspect 59 is passenger detection system,wherein the impedance conversion circuit is comprised by an operationalamplifier having an amplification factor of 1.

Aspect 60 of the present invention provides a passenger detectionsystem, wherein the control circuit is comprised of, at least: memorymeans for storing signal data output from the correction interfacecircuit; means for receiving signals output from the antennae interfacecircuit; a correction section for compensating for drift according tocorrection data received; an evaluation section for evaluating passengerseating conditions according to correction results output from thecorrection section. The invention in aspect 61 is a passenger detectionsystem according to one of aspect 54 or 55, wherein the antennaeinterface circuit and the correction interface circuit are comprised by,at least: an electric field generation device; a current detectiondevice for detecting a perturbation current produced by application ofpower by the electric field generation device; wherein the antennaeinterface circuit is connected to an electrode and the correctioncircuit is not connected to an antenna electrode and is open-circuited.

According to the invention presented in aspects 54 to 61, the antennaeinterface circuit and the correction interface circuit have essentiallythe same configuration of circuit components, and the electricgeneration device in the antennae interface circuit is connected to anelectrode while the electric generation device in the correction circuitis not connected to an antenna electrode and is open-circuited.Therefore, output signals Sin, Hin from the respective interfacecircuits are affected by the same level of drift, so that by calculatingthe difference portion D₁ between the output signals Sin, Hin, the driftcomponents in each interface circuit can be eliminated.

In addition, by calculating the output signals Sin, Hin and thedifference portion D₁, essentially true signal data D₂ can be obtainedaccording to a relation D₂=(Hin−(Sin+D₁)). Therefore, even is the outputsignals from the antennae interface circuit are affected over time bythermal effects, passenger seating conditions can always be determinedaccording to correct information data. For example, the system enablesto avoid misdiagnose passenger seating conditions such that even thoughan adult is seated, erroneous judgment indicates that a child is seated.

Further, the control circuit makes judgment based on essentially truesignal data D₂ so that the airbag apparatus can be controlled accordingto correct passenger seating conditions.

Aspect 62 of the present invention provides a passenger detection systemcomprised by antenna electrodes disposed on a seat inside an automobileconnected, using a shielding cable whose signal line is shielded by ashielding line, to a signal processing circuit for detecting passengerseating conditions by processing signal data related to a perturbationcurrent flowing in an antenna electrode resulting from applying anelectric field generated about the antenna electrode, wherein a buffercircuit, for maintaining signal levels of signal line and shield line ata same level, is connected between the signal line and the shield line.

Aspect 63 of the present invention provides a passenger detectionsystem, wherein a plurality of antenna electrodes are disposed on theseat, and antenna electrodes and the signal processing circuit are wiredusing a plurality of shielding cables.

Aspect 64 of the present invention provides a passenger detectionsystem, wherein a common buffer circuit is connected to each of theplurality of antenna electrodes and signal processing circuit through arespective switching element.

In this case, the signal line in the shield cable and the buffer circuitconnected to the shield line are connected to an operational amplifierto maintain the same potential in the signal line and the shield line.This buffer circuit the signal levels in the com circuit are maintainedat the same potential level so that the RC time constant between thesignal and shield lines does not affect the signal communication betweenthe control circuits and the signal error in evaluating the passengerseating conditions can be eliminated.

The buffer circuit can resolve the problems of scatter in the signallevels resulting from the differences in the lengths of the shieldcables, therefore, design freedom is increased by not having to limitthe cable length.

Also, by using a common buffer circuit for a plurality of shield cables,cost is reduced, and in particular, circuit configuration can besimplified significantly for a passenger detection system based on manyantenna electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B are diagrams, respectively, to show basic actions of anoccupant detection system with an electric field distribution of anantennae, and an electric field distribution of the antennae with anearby object.

FIGS. 2A, 2B are diagrams of the interior section of the passengerdetection system showing, respectively, a side view of the antennaelectrodes installed on the seat, and a front view of the seat.

FIGS. 3A, 3B, 3C are diagrams of the antenna electrodes shown in FIG. 2,to show, respectively, a plan view, a cross sectional view through X—X,a cross sectional view through Y—Y.

FIGS. 4A, 4B, 4C are diagrams showing, respectively, a plan view, across sectional view through Z—Z and a plan view of another example ofthe coupling conditions of the connection terminals to the antennaelectrodes shown in FIG. 2.

FIG. 5 is a block diagram of the occupant detection system.

FIGS. 6A, 6B are, respectively, a block circuit diagram of the phasedifference detection circuit shown in FIG. 5, and a block circuitdiagram of a waveform shaping circuit.

FIG. 7 is a block circuit diagram of the airbag apparatus shown in FIG.5.

FIGS. 8A, 8B, 8C are diagrams to explain the operation of the phaseshift detection circuit, shown in FIG. 6, in terms of, respectively:output waveforms of the forward signal and first flipflop circuit;waveforms of the output signal and the second flipflop circuit; anddetection of phase differential from the first and second flipflopcircuits.

FIGS. 9A, 9B are diagrams to show, respectively, an adult seatingcondition and a child seating condition.

FIG. 10 is a flowchart for a passenger detection process.

FIG. 11 is a flowchart for the initial process of passenger detection.

FIG. 12 is a flowchart for the signal receiving process shown in FIG.10.

FIG. 13 is a flowchart for the passenger evaluation process shown inFIG. 10.

FIG. 14 is a flowchart for SRS process shown in FIG. 10.

FIGS. 15A, 15B are diagrams for another arrangement of the antennaelectrodes, respectively showing, a front view of an adult passenger,and a front view of a child passenger.

FIG. 16 is a flowchart for the process of detecting a passenger usingthe passenger detection system.

FIG. 17 is a flowchart for the initial process of passenger detection.

FIG. 18 is a flowchart for the signal receiving process.

FIG. 19 is a flowchart for the passenger evaluation process.

FIG. 20 is a flowchart for SRS process.

FIGS. 21A˜21C are diagrams of the specific antenna electrodes structuresshowing, respectively, a plan view, a cross sectional view of theconnection between antenna electrodes and lead wire connection, andanother example of the connection.

FIG. 22 is a perspective view of antenna electrodes details.

FIG. 23 is a plan view of another antenna electrodes.

FIGS. 24A, 24B are, respectively, a plan view and a partial crosssectional view of another antenna electrode.

FIG. 25 is a plan view of a section of the antenna electrodes.

FIG. 26 is a plan view of yet another antenna electrodes.

FIG. 27 is a plan view of still another antenna electrodes.

FIGS. 28A, 28B are, respectively, a block circuit diagram and a circuitdiagram of an electrical field generation circuit and an informationdetection circuit.

FIGS. 29A, 29B are, respectively, a side view and a front view of theantenna electrodes arrangement.

FIGS. 30A, 30B are, respectively, a plan view and a cross sectional viewof the specific structure of the antenna electrodes shown in FIG. 29.

FIG. 31 is a block circuit diagram of the passenger detection system.

FIG. 32 is a block circuit diagram of the airbag apparatus shown in FIG.31.

FIG. 33 is a flowchart for the process of detecting a passenger usingthe passenger detection system.

FIG. 34 is a flowchart for the initial process of passenger detection.

FIG. 35 is a flowchart for the signal receiving process.

FIG. 36 is a flowchart for the passenger evaluation process.

FIG. 37 is a flowchart for SRS process.

FIG. 38 is a plan view of a seat.

FIG. 39 is a front view of another seat.

FIGS. 40A, 40B are diagrams of the interior section of the passengerdetection system showing, respectively, a side view of the antennaelectrodes installed on the seat, and a front view of the seat.

FIGS. 41A˜41C are diagrams of specific structures of the antennaelectrodes showing, respectively, a plan view, a cross sectional view ofkey parts, and a plan view of another embodiment.

FIG. 42 is a cross sectional view of the essential parts to show thecoupling condition between the connection terminal and the antennaelectrode shown in FIG. 41B.

FIG. 43 is a block circuit diagram of the passenger detection system.

FIG. 44 is a block circuit diagram of a specific example of theoscillation circuit shown in FIG. 43.

FIG. 45 is a block circuit diagram of a specific example of the phaseshift detection circuit shown in FIG. 43.

FIG. 46 is a block circuit diagram of the airbag apparatus shown in FIG.43.

FIGS. 47A, 47B, 47C are diagrams to explain the operation of the phaseshift detection circuit, shown in FIG. 45, in terms of, respectively:output waveforms of the forward signal and first flipflop circuit;waveforms of the output signal and the second flipflop circuit; anddetection of phase differential from the first and second flipflopcircuits.

FIGS. 48A, 48B are diagrams to show, respectively, an adult seatingcondition and a child seating condition.

FIG. 49 is a flowchart for the process of detecting a passenger usingthe passenger detection system.

FIG. 50 is a flowchart for the initial process of passenger detectionshown in FIG. 49.

FIG. 51 is a flowchart for the signal receiving process shown in FIG.49.

FIG. 52 is a flowchart for the passenger evaluation process shown inFIG. 49.

FIG. 53 is a flowchart for SRS process shown in FIG. 49.

FIGS. 54A, 54B are diagrams for another arrangement of the antennaelectrode, respectively showing, a front view of an adult passenger, anda front view of a child passenger.

FIGS. 55A, 55B are diagrams of the interior section of the passengerdetection system showing, respectively, a side view of the antennaelectrodes installed on the seat, and a front view of the seat.

FIGS. 56A˜56C are diagrams of specific structures of the antennaelectrodes showing, respectively, a plan view, a cross sectional view ofkey parts, and a plan view of another embodiment.

FIG. 57 is a cross sectional view of the essential parts to show thecoupling condition between the connection terminal and the antennaelectrode shown in FIG. 56B.

FIG. 58 is a block circuit diagram of the passenger detection system.

FIG. 59 is a block circuit diagram of the airbag apparatus shown in FIG.58.

FIGS. 60A˜60D are diagrams to explain the operation of the control unit,in terms of respectively: gate signal output from the control circuit;waveform of forward signal when the seat is vacant (output waveform ofelectric field generator); waveform of forward signal when the seat isoccupied (output waveform of electric field generator); and dc. outputcurrent in ac-dc conversion circuit.

FIGS. 61A, 61B are diagrams to show, respectively, an adult seatingcondition and a child seating condition.

FIG. 62 is a flowchart for the process of detecting a passenger usingthe passenger detection system.

FIG. 63 is a flowchart for the initial process of passenger detectionshown in FIG. 62.

FIG. 64 is a flowchart for the signal receiving process shown in FIG.62.

FIG. 65 is a flowchart for the passenger evaluation process shown inFIG. 62.

FIG. 66 is a flowchart for SRS process shown in FIG. 62.

FIG. 67 is a block circuit diagram 610A of the passenger detectionsystem.

FIG. 68 is a block circuit diagram 610B of the passenger detectionsystem.

FIG. 69 is a block circuit diagram 610C of the passenger detectionsystem.

FIG. 70 is a block circuit diagram 610D of the passenger detectionsystem.

FIGS. 71A, 71B are diagrams of another arrangement of the antennaelectrodes showing, respectively, a front view of an adult sitting; anda front view of a child sitting.

FIGS. 72A˜72C are diagrams of an arrangement of the antenna electrodeson the seat, showing respectively: a cross sectional side view of keyparts; a partial broken plan view of a section; and a plan view of anopen antennae.

FIG. 73 is an electrical circuit diagram of the passenger detectionsystem.

FIG. 74 is a circuit diagram of the airbag apparatus in the system shownin FIG. 73.

FIGS. 75A˜75D are diagrams to explain the operation of the control unit,in terms of respectively: gate signal output from the control circuit;waveform of forward signal when the seat is vacant (output waveform ofelectric field generator); waveform of forward signal when the seat isoccupied (output waveform of electric field generator); and dc. outputcurrent in ac-dc conversion circuit.

FIGS. 76A, 76B are diagrams to show, respectively, an adult seatingcondition and a child seating condition.

FIGS. 77A, 77B are circuit diagrams of the passenger detection systemshowing respectively: block circuit diagram; and a specific circuitdiagram of an interface circuit.

FIG. 78 is a graph of output signals from the interface circuit forantenna electrodes and correction shown in FIG. 77.

FIG. 79 is a flowchart for the process of detecting a passenger usingthe passenger detection system.

FIG. 80 is a flowchart for the initial process of passenger detectionshown in FIG. 79.

FIG. 81 is a flowchart for the signal receiving process shown in FIG.79.

FIG. 82 is a flowchart for the passenger evaluation process shown inFIG. 79.

FIG. 83 is a flowchart for SRS process shown in FIG. 79.

FIG. 84 is a schematic side view of another embodiment of the passengerdetection system.

FIG. 85 is an electrical circuit diagram for the system shown in FIG.84.

FIG. 86 is a block circuit diagram for the system shown in FIG. 84.

FIGS. 87A, 87B are diagrams to explain the basic operation of thepassenger detection system in terms of electric field distributionpatterns between the antenna electrodes, respectively, when an objectdoes not or does intervene between the electrodes.

FIGS. 88A, 88B are diagrams to explain the basic operation of otherpassenger detection system in terms of the electric field distributionpatterns of an antenna electrode, respectively, when an object does notor does intervene between the electrodes.

FIG. 89 is a perspective view of a seat equipped with the passengerdetection system.

FIG. 90 is a block circuit diagram of the passenger detection circuitinstalled in the seat shown in FIG. 89.

FIG. 91 is a block circuit diagram of a specific example of the circuitshown in FIG. 90.

FIG. 92 is a block circuit diagram of an embodiment of the passengerdetection system.

FIG. 93 is a schematic drawing of the shield cable of the system shownin FIG. 92.

FIG. 94 is a block circuit diagram of a specific example of the circuitshown in FIG. 92.

FIG. 95 is a block circuit diagram of another specific example of thecircuit shown in FIG. 92.

FIG. 96 is a block circuit diagram of a conventional airbag apparatus.

FIG. 97 is a block circuit diagram of an improved conventional airbagapparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

The basic principle of the passenger detection system will be explainedwith reference to FIG. 1. The present detection system is based onperturbation in weak electric field generated by the presence of anobject in the vicinity of antenna electrode. First, as shown in FIG. 1A,when a high frequency low voltage (HFLV) signal is impressed on anantenna E1 by an oscillation circuit OSC, a weak electric field isgenerated in the vicinity of the electrode, resulting in a flow ofcurrent I in the antenna electrode E1. When an object OB is introducedin the vicinity of the antenna electrode E1, as shown in FIG. 1B, theelectric field is disturbed, resulting in a perturbation current I₁,which is different in character than current I.

Therefore, by utilizing the fact that the different currents flow inantenna electrode E1, depending on there is or there is no object OB ona vehicle seat, it is possible to detect the seating condition of thepassenger. Specially, by increasing the number of antenna electrodes,much more precise information can be gained on the object, including apassenger, that is loading the seat. When the object OB is on the seat,the perturbation current in the antenna electrode E1 increases whilewhen the object OB is not on the seat, the perturbation current in theantenna electrode E1 is decreased.

Next, the passenger detection system based on this principle will beexplained with reference to FIGS. 2˜7. The parts of the present systemwhich are the same as those in the conventional systems shown in FIGS.96, 97 are referenced using the same reference numerals and theirexplanations are omitted. FIGS. 2˜4 show the structures of thepassenger/driver seat and the antenna electrodes, and seat 1 iscomprised primarily of a sitting section 1 a and a backrest section 1 b.Sitting section 1 a is typically comprised by a seat frame 3 fixed to abase 2 that is slidable forward and backward, a cushion part disposedabove the seat frame 3, and an outer covering for the cushion part, andthe backrest section 1 b is typically comprised by a cushion partdisposed on the front side of the seat frame 3 and an outer covering. Apart of the detection system is comprised by a plurality of antennaelectrodes 4 (4 a˜4 d) of substantially the same shape and size arrangedsymmetrically (for example rectangle) on the sitting section 1 a. It isallowable to install the antenna electrodes 4 on the outside of thecovering or on the covering part itself. Also, a control unit 10 may beprovided on the seat frame 3 or in the vicinity.

The antenna electrode 4 is made of a conductive fabric but it may bemade by weaving a metallic thread in the seat fabric of the sittingsection 1 a or applying a conductive paint or using metal strips. It ispreferable that the antenna electrodes 4 be constructed by arrangingseparate rectangle-shaped electrodes of substantially the same size,such as those antenna electrodes 4 a˜4 d shown in FIG. 3, as a unit onone surface of a base member 5 made of an insulating material such asnon-woven cloth, so that they may be placed inside of the outer coveringpart of the sitting section 1 a. Lead wire 6 (6 a˜6 d) including shieldwires are independently provided for each of the antenna electrodes 4a˜4 d, and are connected to the connectors (or terminals) 19 a˜19 d ofthe control unit 10, which will be described later.

An example of the connections between the antenna electrodes 4 (4 a˜4 d)and the lead wires 6 (6 a˜6 d) is shown in FIG. 4. Connecting structuresare all the same for the antenna electrodes 4 a˜4 d and the lead wires 6a˜6 d, therefore, the following explanation will be based on connectingan antenna electrode 4 a to a lead wire 6 a. As shown in FIGS. 4A and4B, a connection terminal 7 is riveted through the antenna electrode 4 aand the base member 5. A terminal lug 8 is attached to the connectionterminal 7 prior to riveting, so that an electrical connection is madebetween the terminal lug 8 to the antenna electrode 4 a through theconnection terminal 7. The terminal lug 8 is connected so as to make amechanical and electrical contact with the lead wire 6 a using afastening means such as pressure lug 9. The connection between theantenna electrode 4 a and the lead wire 6 a may be made by providing anextension member 4 aa at a portion of the antenna electrode 4 a andjoining to the connection terminal 7.

As shown in FIG. 5, a control unit 10, disposed on the seat frame 3 orits vicinity, is comprised by, for example: an electric field generationdevice (oscillator and the like) 11 for generating a weak electric fieldin the vicinity of the antenna electrodes 4 a˜4 d; an amplitude controlcircuit 12 for controlling the amplitude of the forward signal outputfrom the oscillation circuit 11 to antenna electrode 4 approximatelyconstant; an information detection circuit (current detection circuitfor example) 15 for detecting information related to the forward currentof the forward signal; an ac-dc conversion circuit 16 for converting theoutput signal in the current detection circuit 15 to direct current (dchereinbelow); an amplifier 17 for amplifying the output signal from theac-dc conversion circuit; a switching circuit 18 having a plurality ofswitching devices 18 a˜18 d for the antenna electrodes 4 a˜4 d,connected to the current detection circuit 15; connectors 19 a˜19 ddisposed in the housing of the control unit, connected to the switchingdevices 18 a˜18 d of the switching circuit 18; a phase shift detectioncircuit 20 connected to the amplitude control circuitry (signalgenerating side) and the switching circuitry (antenna electrode side) ofthe current detection circuit 15, for detecting a phase shift betweenthe forward signal from the oscillation circuit and the applicationsignal to the antenna electrodes; an amplifier 21 for amplifying theoutput signal of the phase shift detection circuit 20; a control circuit22 including MPU and the like; connector 23 connected to the batterysource (not shown) disposed in the housing; and an electric powercircuit 24 connected between the connector 23 and the control circuit 22and others. An airbag apparatus 30, of a configuration such as the oneshown in FIG. 7, is connected to control circuit 22 of the control unit10. The oscillation circuit 11 is designed to generate HFLV signals witha voltage range 5˜10 volts at a frequency of 120 KHz, for example.Selective switching of the switching devices 18 a˜18 d is carried outaccording to output signals from the control circuit 22.

In the control unit 10, the amplitude control circuit 12 includes anamplitude varying circuit 13 for varying the voltage amplitude of theforward signals, and amplitude detection circuit 14 for detecting thevoltage amplitude of the forward signals. The amplitude varying circuit13 is comprised by an amplitude varying section 13 a including aprogrammable gain amplifier (PGA) and others, and the amplitudedetection circuit 14 is comprised by: a voltage amplitude detectionsection 14 a having an op-amp; an ac-dc conversion circuit 14 b forconverting the output signal from the amplitude detection circuit 14 ato dc; and an amplifier for amplifying the output signal from the ac-dcconversion circuit 14 b. Output signal from the amplifier 14 c issupplied to the control circuit 22, and the amplitude varying signal forthe amplitude varying section 13 a is output from the control circuit22.

The current detection circuit 15 in the control unit 10 includes animpedance element, for example resistor 15 a, connected in series to thesignal circuit (forward signal side) and an amplifier 15 b, such asdifferential amplifier, for amplifying the terminal voltage of theresistor 15 a. The output side of the current detection circuit 15 isconnected to the control circuit 22 through the ac-dc conversion circuit16 and the amplifier 17. The output side of the resistor 15 a in thecurrent detection circuit 15 is connected to the connectors 19 a˜19 dthrough the switching circuit 18.

Further, an example of the phase shift detection circuit 20 is shown inFIG. 6A, which is comprised by: wave shaping circuits 20 a for shapingthe output wave of the forward signal from the oscillation circuit 11and the application signal to the antenna electrodes 4 (4 a˜4 d)separately to shape the waveform from sine waves to rectangular waves; afirst flipflop (shortened to ff) circuit 20 b 1; a second if circuit 20b 2; and an integration circuit 20 e. An example of the wave shapingcircuits 20 a is shown in FIG. 6B. It should be noted that when the HFLVsignals output from the oscillation circuit 11 are generated by suchmeans as switching of a single dc source, say, +5 volts (that is, theoutput voltage is rectangular), then the wave shaping currents 20 a maybe omitted.

The passenger detection system having the above structure operates inthe following manner. First, the oscillation circuit 11 generates HFLVsignals whose voltage amplitude is detected by the detection section 14a of the amplitude detection circuit 14, and the detection signal isconverted to a dc signal in the ac-dc conversion circuit 14 b, and theamplified signal from the amplifier 14 c is input in the control circuit22. The control circuit 22 judges whether the detected voltage amplitudemeets the required amplitude value, and sends the amplified signal tothe amplitude varying section 13 a to correct the amplitude to therequired value. This process controls the voltage amplitude of theforward signal at a given voltage amplitude, and henceforth, voltageamplitude of the forward signal is corrected to a given amplitude by thelinked action of the amplitude varying circuit 13 and the amplitudedetection circuit 14.

The forward signal having a constant voltage amplitude is applied toantenna electrodes 4 (41˜Ad) through the current detection circuit 15,switching circuit 18 (18 a˜18 d), connectors 19 a˜19 d, resulting in thegeneration of a weak electric field in the vicinity of the antennaelectrodes 4 (4 a˜4 d). In this process, switching circuits 18 areoperated by signals from the control circuit 22 so that, first, only theswitching device 18 a is closed, next only the switching device 18 b isclosed, next only the switching circuit 18 c is closed, and such astepwise switching is successively carried out so that when a particularswitch is being closed, other switches are all opened. Therefore, when aparticular switching device of the switches (18 a˜18 d) is closed,constant-amplitude forward signal passes through a particular switchingdevice (18 a˜18 d), a particular connector (19 a˜19 d) and reaches aparticular antenna electrode (4 a˜4 d), generating an electric field inthe vicinity of a particular antenna electrode (4 a˜4 d), so thatdifferent values of perturbation current, governed by the seatingcondition of the passenger, flows in the antenna circuits. Theperturbation current is detected by the current detection circuit 15,converted to a dc signal in the ac-dc conversion circuit 16, amplifiedin the amplifying circuit 17 and is successively input in the controlcircuit 22. The sequence of switching may be in a reverse direction, 18d, 18 c . . . to 18 a.

The signal (voltage) at both input/output ends of the current detectioncircuit 15, that is, the forward signal from the oscillation circuit 11in the oscillation control circuitry and the application signal to theantenna electrodes 4 (4 a˜4 d) in the switching circuitry (antennaelectrode side) are input in the phase shift detection circuit 20. Thesine wave signals are converted to rectangle waves, as shown in FIG. 8A,by the wave shaping circuit 20 a, and are output to the first and secondif circuits 20 b 1, 20 b 2. The leading edge (arrow) of the rectanglewave output from the forwarding side is detected at the terminal CK ofthe first if circuit 20 b 1, and the terminal bar Q outputs a “high”. Inthe meantime, in the receiving side also, the leading edge (arrow) ofthe rectangle wave is detected at the terminal B of the second ifcircuit 20 b 2, and the terminal bar Q outputs a one-shot low signalmomentarily. When this output signal is input in the terminal RES of thefirst if circuit 20 b 1, the output signal of the terminal bar Q of thefirst if circuit 20 b 1 is inverted to a low, as shown in FIG. 8G. Thisoutput signal represents the amount of phase difference (phase shift),and is converted to a voltage value by being integrated in theintegration circuit 20 c, and is input in the control circuit 22 throughthe amplifier 21. The phase shift detection is carried out successivelyto correspond with the detection of forward current to each antennaelectrode by the current detection circuit 15.

In the control circuit 22, reference data are already stored such asthreshold values (threshold data) regarding the seating conditions(passenger loading and passenger identify, whether adult/child),threshold values regarding the phase difference between the forwardsignal to the current detection circuit 15 and the application signal tothe antenna electrodes (threshold data). Specifically, passenger loadingdata are selected as follows. For example, as shown in FIGS. 9A, 9B,when an adult passenger P or a child passenger SP is seated on the seat1, the areas opposing the individual antenna electrodes are different,and as a result, the levels of the current flowing in the antennaelectrodes are different, such that when an adult passenger P is seated,the current level is higher than that when a child passenger SP isseated. Therefore, a threshold value, which is somewhat lower than thecurrent level for a child passenger SP, is selected as the thresholdvalue for passenger loading. Thus, when detected data is higher than thethreshold value, it is assumed that a passenger is seated, and when itis lower than the threshold value, it is assumed that no one is seated.It is preferable that the threshold value be selected according to a sumof all the current flowing in each antenna electrode, but it is possibleto select a threshold value for each antenna electrode.

Identity of a passenger is determined as follows. When an adultpassenger P or a child passenger SP is seated, the levels of the currentflowing in individual antenna electrodes are different as explainedabove. Therefore, the threshold value for the identity of the passenger(whether the passenger is an adult or a child) is selected as a currentlevel midway between the adult and child threshold values. Thus, whendetected data is higher than the threshold value, it is assumed that apassenger is seated, and when it is lower than the threshold value, itis assumed that no one is seated. It is preferable that the thresholdvalue be selected according to a sum of all the current flowing in eachantenna electrode, but it is possible to select a threshold value foreach antenna electrode.

With respect to selecting a threshold value for the phase difference, asuitable value may be chosen between an average value of the phasedifference detected by the phase shift detection circuit 20 when aperson is present, and an average value of the phase difference, causedby factors other than a human body. The characteristics of the seat(wetness, for example) can affect the measurements, therefore, upper andlower limits of threshold values are chosen, so that when the phasedifference data are inside the range, it is assumed that a person isseated. Therefore, pre-stored data (regarding the passenger seatingconditions and the phase difference) and the detected data (regardingthe current levels and the phase difference) are compared in the controlcircuit 22 to determine whether a seated passenger is an adult or achild, and what the characteristics of the seat are.

Thus, signal data received by the control circuit 22 are comparedagainst the threshold data stored in the control circuit 22, so thatwhen the current levels in all the antenna electrodes 4 a˜4 d are high,it is assumed that seat 1 has a passenger and that the passenger is anadult P, as illustrated in FIG. 9A. In such a case, the control circuit22 places the airbag circuit shown in FIG. 7 in the deployable state.When the current levels in all the antenna electrodes 4 a˜4 d are lowand are lower than the passenger loading threshold value, it is assumedthat seat 1 has a passenger and that the person is a child SP, asillustrated in FIG. 9B. In such a case, the airbag apparatus 30 in FIG.7 is placed in the not-deployable state by the control signal fromcontrol circuit 22. That is, when the airbag is not to be deployed, thecontrol circuit 22 instructs the control circuit CC in the airbagapparatus 30 so that a gate signal is not supplied to the switchingelement SW2 of the passenger side when a collision takes place. Thedriver-side switching element SW1 is supplied with a gate signal. Whenthe driver and an adult are seated, the switching elements SW1, SW2 areboth placed in the deployable state.

The overall process of operation of the passenger detection system willbe explained with reference to the overall flowchart shown in FIG. 10.FIGS. 11˜14 relate to steps in sub-processes. First, as shown in FIG.10, the ignition circuit is turned on so that the process is in START.In step S1, the program is initialized, and proceeds to step S2. In stepS2, initial diagnostics are performed for any communication problemsbetween the control circuit 22 and the airbag apparatus 30. In step S3,it examines whether the engine is operating, and if it is judged thatthe engine is operating, it proceeds to step S4. If it is judged thatthe engine is not operating, the program is shutoff. In step S4, signaldata related to perturbation current flowing in a particular antennaelectrode and signal data on phase shift related to passenger seatingconditions, resulting from the application of a weak electric field on aparticular antenna electrode of the antenna electrodes 4 a˜4 d, arereceived in the control circuit 22. In step S5, based on the receiveddata, passenger loading data, passenger identity data are examined andconclusions reached. In step S6, SRS process (for placing the airbag ineither the deployable state or not-deployable state) is carried outbetween the control circuit 22 and the airbag apparatus (SRS) 30. Whenstep S6 is completed, it returns to step S4 and repeats the steps S4 toS6. Step S3 may be omitted.

Initial diagnostics are carried out as outlined in FIG. 11. First, instep SA1, stored data are sent from the control circuit 22 to thecontrol circuit CC in the airbag circuit 30. In step SA2, passenger dataare received from the airbag apparatus 30. In step SA3, it is examinedwhether the received data from the airbag apparatus 30 match the storeddata. If it is judged that the data are matched, the process iscontinued. If the data do not match, it is judged that problems exist inthe com circuit and fail-safe process is carried out and alert lamp isturned on, for example. The initial diagnostics may be carried out bysending the stored data from the airbag apparatus 30 to the controlcircuit 22 so that matching process can be carried out in the controlcircuit CC in the airbag apparatus 30.

Signal reception process is carried out as outlined in FIG. 12. First instep SB1, the control circuit 22 successively selects one switchingdevice at one time from the switching devices 18 a˜18 d so that only theswitching circuit 18 a is closed, for example, to select an antennaelectrode 4 a. In step SB2, the data from the respective antennaelectrode and phase difference are received in the control circuit 22.In step SB3, it is examined whether successive selection of antennaelectrodes 4 a˜4 d by the successive actions of the switching devices 18a˜18 d has been completed. If it is judged that the switching processhas been completed, it proceeds to passenger evaluation process. If itis judged that the switching process is incomplete, it returns to stepSB1.

The passenger evaluation process is carried out as outlined in FIG. 13.First, in step SC1, signal data related to the current levels flowing inall the antenna electrodes 4 a˜4 d and threshold values related to thepassenger seating conditions are compared to decide whether the measuredsignal data are higher than the threshold values. If the measured signaldata are higher than the threshold values, it proceeds to step SC2, andif it is judged that the signal data are not higher, it proceeds to stepSC3. In step SC2, if it is judged that the passenger sitting on the seatis an adult, it proceeds to step SC4, so that ON-data for placing theairbag apparatus 30 in the deployable state are entered in the SRSprocess, and the program connects to SRS process. Also, in step SC3, ifthe passenger sitting on the seat is a child, it proceeds to step SC5,and OFF-data for not deploying the airbag apparatus 30 are entered inthe SRS process, and the program is continued.

The SRS process is carried out as outlined in FIG. 14. First, in stepSD1, ON-data for placing the airbag apparatus in the deployable state orOFF-data for placing the airbag apparatus in the not-deployable stateand system check-data are sent from the passenger detection unitcircuitry (control circuit 22) to the airbag apparatus circuitry(control circuit CC). In step SD2, (system) OK-data or (system) NG-datain response to the ON-data and OFF-data and system check-data from theairbag apparatus are received by the control circuit 22, and it proceedsto step SD3. In step SD3, it is judged whether the ON-/OFF-data andsystem check-data, which had been sent from the passenger detection sideto the airbag apparatus circuitry, are again returned from the airbagapparatus circuitry to the passenger detection side in the normalcondition. If it is judged to be normal (no problems in signal circuit),the process is continued. If there is a problem in the com circuit, itproceeds to step SD4, and it is examined whether the fail-safe timer isat zero. This detection process of circuit problems is programmed torepeat three times. Therefore, if it is judged that the fail-safe timeris zero, fail-safe process is carried out, and a warning lamp isactivated, for example. If it is judged that the fail-safe timer is notat zero, it proceeds to step SD5, and fail-safe timer count isperformed, and the process is continued.

On the other hand, in step SE1, the airbag apparatus circuitry (controlcircuit CC) receives ON-data for placing the airbag apparatus in thedeployable state or OFF-data for placing the airbag apparatus in thenot-deployable state and system check-data from the passenger detectionunit circuitry (control circuit 22). In step SE2, the received data arechecked to examine whether or not they are normal. In either case, itproceeds to step SE3 for sending OK-data or NG-data and systemcheck-data to the passenger detection unit circuitry. If it is judged,in step SE2, that the signal circuit is normal, OK-data are sent in stepSE3, and it proceeds to step SE4. In step SE4, the data on the airbagside is renewed in response to the OK-data, thereby enabling to placethe airbag in the deployable state or not-deployable state. If, in stepSE2, it is judged that there is a problem in the com circuit, NG-dataare sent to the control circuit 22 in step SE3, and it proceeds to stepSE5. In step SE5, it is examined whether the fail-safe timer is at zero.This detection process of circuit problems is programmed to repeat threetimes. Therefore, if it is judged that the fail-safe timer is zero,fail-safe process is carried out, and a warning lamp is activated, forexample. If it is judged that the fail-safe timer is not at zero, itproceeds to step SE6, and fail-safe timer count is performed, and theprocess is continued.

According to this embodiment, a plurality of antenna electrodes 4 (4 a˜4d) are disposed separately on the sitting section of seat 1, therefore,each antenna electrode is successively connected to the oscillationcircuit 11 by successively switching the switching devices 18 a˜18 d inthe switching section 18, and by impressing HFLV to generate a weakelectric field, a particular value of current, determined by theopposing area of contact with the passenger and other factors, flows ineach antenna electrode 4. Therefore, by detecting the values of suchperturbation current, it is possible to detect readily whether thepassenger is an adult or a child.

Especially, many antenna electrodes 4 a˜4 d can be excited bysuccessively applying HFLV signals generated by the oscillation circuit11 by means of switching devices 18 a˜18 d in the switching circuit 18,the circuit structure is simplified and the cost of the system islowered.

Also, because many antenna electrodes 4 a˜4 d are disposed symmetricallyin the sitting section 1 a, it is possible to detect if the passengerposition is shifted laterally, on the basis of the values of the currentflowing in each antenna electrode.

Furthermore, the phase difference between the forward signals (from theoscillation circuitry to the amplitude control circuitry) and the outputsignals (from the antenna electrode circuitry to antenna electrode 4) isdependent on the nature of the object sitting on the seat 1.Particularly, the levels of phase difference are recognizably differentwhen the object is a human body. Therefore, the use of the phase shiftdetection circuit 20 to detect the phase difference together with theresult of passenger identity judgment based on signal data related topassenger identity by detected perturbation current levels, enables toreliably detect passenger loading on the seat 1.

In particular, the airbag in the airbag apparatus 30 is able to be madeeither deployable or not deployable, depending on the judgment of thesystem on whether the passenger is an adult or a child. For example, ifit is judged that the passenger is a child based on a low-level ofdetected current, the airbag in the airbag apparatus 30 is placed in anon-deployable state. Therefore, even if the car collides, the airbag isnot opened and the child is prevented from suffering secondary injuries.

Also, the system cost can be lowered significantly by providing thesystem power source from the single power source produced by theelectric power circuit 24, and by producing approximate HFLV rectanglewaveforms with the use of only the positive power source in theoscillation circuit 11 in the control circuit 10.

Further, the amplitude control circuit 12 is used to maintain theamplitude of the voltage impressed on the antenna electrodes 4 (4 a˜4 d)approximately constant, so that the data related to perturbation currentprovided by the electric current detection circuit 15 can be comparedreadily with the threshold data relating the passenger seatingconditions and others, and a judgment arrived at with a high degree ofaccuracy and reliability.

FIG. 15 shows another embodiment of the passenger detection system. Thissystem is basically the same as the system presented above, but thedifference is that the antenna electrodes 4 (4 a˜4 b) are provided onthe backrest section 1 b, and they are not provided on the sittingsection 1 a.

As shown in FIG. 15A, when the opposing areas to all the antennaelectrodes 4 a˜4 d are wide, and the detected current levels are high,it is judged that the passenger sitting on the seat 1 is an adult. Also,as shown in FIG. 15B, when the opposing areas to all the antennaelectrodes 4 a˜4 d are small, and the detected current levels are low,it is judged that the passenger sitting on the seat 1 is a child.

It should be noted that the present invention is not limited to theabove embodiments and other arrangements are possible. For example, thenumber of antenna electrodes may be adjusted suitably, and their shapecan be rectangular, strip shape which are possible examples. Electricfield generation device may include an HFLV source to producesubstantially rectangle waveform by switching of positive electricalpower source based on clock signals in the control circuit, or bydividing the clock signal in the control circuit. The output frequencyother than 120 KHz may be chosen depending on the conditions inside thecar, and the voltage may be selected outside the range of 5˜12 volts.Also, the amplitude control circuit and the phase shift detectioncircuit may be omitted depending on the precision of the system powersource and expected performance level of the system. Also, informationdetection circuit includes not only the embodied example of directdetection of the antennae current, but includes such indirect detectionbased on information on voltages related to the perturbation current andwaveform data. Further, passenger evaluation methods include comparisonof stored data related to the seating pattern and sitting posture of thepassenger with the detected data, thereby judging the passenger identitycriteria such as passenger loading, and whether the passenger is anadult or a child.

Embodiment 2

Next, Embodiment 2 will be presented using the same reference numeralsas those in Embodiment 1 for those parts that are the same, and theirexplanations are omitted. The passenger detection system in thisembodiment is based on detecting the perturbation current related topassenger seating conditions by comparison of reference data withdetected data and using improved switching methods.

As shown in FIG. 5, a control unit 10 is disposed on the seat frame 3 orits vicinity, and this control unit 10 is comprised by, for example: anelectric field generation device (oscillator and the like) 11 forgenerating a weak electric field; an amplitude control circuit 12 forcontrolling the amplitude of the forward signal from the oscillationcircuit 11 to antenna electrode 4 approximately constant; an informationdetection circuit (current detection circuit for example) 15 fordetecting information on the forwarding current of the forward signal;an ac-dc conversion circuit 16 for converting the output signal in thecurrent detection circuit 15 to dc; an amplifier 17 for amplifying theoutput signal from the ac-dc conversion circuit; a switching circuit 18for the antenna electrodes 4 a˜4 d, connected to the current detectioncircuit 15 and having a plurality of switching devices 18 a˜18 d;connectors 19 a˜19 d disposed in the housing of the control unit,connected to the switching devices 18 a˜18 d of the switching circuit18; a phase shift detection circuit 20 connected to the amplitudecontrol circuit circuitry (oscillation circuitry) and the switchingcircuit circuitry (antenna electrode side) of the current detectioncircuit 15, for detecting the phase difference between the forwardsignal from the oscillation circuit and the application signal to theantenna electrodes; an amplifier 21 for amplifying the output signal ofthe phase shift detection circuit 20; a control circuit 22 includingMPU, external memory (EEPROM for example) and the like; a connector 23connected to the battery source (not shown) disposed in the housing; andan electric power circuit 24 connected between the connector 23 and thecontrol circuit 22 and others. Power source Vcc generated in theelectric power circuit 24 is a constituting element for the control unit10, and is supplied to all the elements requiring power source Vcc. Anairbag apparatus 30, of a configuration such as the one shown in FIG. 7,is connected to control circuit 22 of the control unit 10. Theoscillation circuit 11 is designed to generate HFLV signals at afrequency of 120 KHz, for example. Selective switching of the switchingdevices 18 a˜18 d is carried out according to the output signal from thecontrol circuit 22.

In the control circuit 22, in the reference state (for example, nopassenger sitting in seat 1), signal data related to the initial currentflowing in individual antenna electrodes 4 a˜4 d are stored as initialdata (initial data or vacant seat data) SDn, where n is anidentification number of an antennae 4 a˜4 d in this embodiment in theexternal memory (memory section). Essentially true data DTn (=DSn−ADn)is obtained by subtracting the measured signal data ADn received fromthe current detection circuit 15 from the initial data SDn. Basically,initial data SDn are entered only at the time of new car shipment. Inthe memory section of the control circuit 22 are stored reference dataderived from true data DTn, such as threshold values (threshold data)regarding the seating conditions (detect passenger loading, and identifyadult/child), threshold values regarding the phase difference betweenthe forward signal to the current detection circuit 15 and theapplication signal to the antenna electrodes (threshold data).

Specifically, passenger loading data are selected as follows. Forexample, as shown in FIGS. 9A, 9B, when an adult passenger P or a childpassenger SP is seated on the seat 1, the areas opposing the individualantenna electrodes are different, and as a result, the levels of thecurrent flowing in the antenna electrodes are different, such that whenan adult passenger P is seated, the current level is higher than thatwhen a child passenger SP is seated. Therefore, a threshold value, whichis somewhat lower than the current level for a child passenger SP, isselected as the threshold value for passenger loading. Thus, when thedetected data (DTn) is higher than the threshold value, it is assumedthat a passenger is seated, and when it is lower than the thresholdvalue, it is assumed that no one is seated. It is preferable that thethreshold value be selected according to a sum of all the currentflowing in each antenna electrode, but it is possible to select athreshold value for each antenna electrode.

The identity of a passenger is determined as follows. When an adultpassenger P or a child passenger SP is seated, as shown in FIGS. 9A, 9B,the levels of the current flowing in individual antenna electrodes aredifferent as an adult passenger P produces a higher current than a childpassenger SP. Therefore, the threshold value for the identity of thepassenger is selected as a current level midway between the adult andchild threshold values. Thus, when detected data (DTn) is higher thanthe threshold value, it is assumed that the passenger seated is an P,and when it is lower than the threshold value, it is assumed that thepassenger seated is a child SP. It is preferable that the thresholdvalue be selected according to a sum of all the current flowing in eachantenna electrode, but it is possible to select a threshold value foreach antenna electrode.

With respect to selecting a threshold value for the phase difference, asuitable value may be chosen between an average value of the phasedifference detected by the phase shift detection circuit 20 when aperson is present, and an average value of the phase difference, causedby factors other than a human body. The characteristics of the seat(wetness, for example) can affect the measurements, therefore, upper andlower limits of threshold values are chosen, so that when the phasedifference data are inside the range, it is assumed that a person isseated. Therefore, pre-stored data (regarding the passenger seatingconditions and the phase difference) and the detected data (regardingthe current levels and the phase difference) are compared in the controlcircuit 22 to determine whether a seated passenger is an adult or achild, and what the characteristics of the seat are.

Regarding the phase difference, a suitable value may be chosen betweenan average value of the phase difference detected by the phase shiftdetection circuit 20 when a person is present, and an average value ofthe phase difference, caused by factors other than a human body. Thecharacteristics of the seat (wetness, for example) can affect themeasurements, therefore, upper and lower limits of threshold values arechosen, so that when the phase difference data are inside the range, itis assumed that a person is seated. Therefore, pre-stored data(regarding the passenger seating conditions and the phase difference)and the detected data (regarding the current levels and the phasedifference) are compared in the control circuit 22 to determine whethera seated passenger is an adult or a child, and what the characteristicsof the seat are.

Thus, measured signal data ADn, regarding passenger seating conditions,received by the control circuit 22 are processed with initial seat dataSDn stored in the control circuit 22, and compared against the thresholddata such as passenger loading, so that when the current levels in allthe antenna electrodes 4 a˜4 d are high, it is assumed that seat 1 has apassenger and that the passenger is an adult P, as illustrated in FIG.9A. In such a case, the control circuit 22 places the airbag circuitshown in FIG. 7 in the deployable state. When the current levels in allthe antenna electrodes 4 a˜4 d are low and are lower than the passengerloading threshold value, it is assumed that seat 1 has a passenger andthat the person seated in a child SP, as illustrated in FIG. 9B. In sucha case, the control circuit 22 places the airbag circuit shown in FIG. 7in the not-deployable state. Specifically, when the airbag is not to beactivated, the control circuit 22 instructs the control circuit CC inthe airbag apparatus 30 so that a gate signal is not supplied to theswitching element SW2 of the passenger side when a collision takesplace. The driver-side switching element SW1 is supplied with a gatesignal. When an adult and a child are seated, the switching elementsSW1, SW2 are both selected to be in the deployable state.

The process of passenger detection system will be explained withreference to the flowcharts shown in FIGS. 16˜20. First, as shown inFIG. 16, the ignition circuit is turned on so that the process is inSTART. In step S201, CPU in the control circuit 22 is initialized (forexample, clearing memories, selecting time data and others) and proceedsto step S202. In step S202, to carry out subtraction processing, signaldata related to the initial currents flowing in the antenna electrodes(sensors) 4 a˜4 d in the reference state such as vacant seat 1 arereceived, and the data are written to external memories such as EEEPROMas the initial values SDn, and it proceeds to step S203. In step S203,initial diagnostics are carried out to detect any problems in thecommunication line (com line) between the control circuit 22 and theairbag apparatus 30. In step S204, based on, measured signal data ADn(perturbation current flowing in the particular electrode resulting fromthe application of the weak electric field generated by a particularantenna electrode of the antenna electrodes 4 a˜4 d) and phase shiftdata related to passenger seating conditions are received in the controlcircuit 22. In step S205, it is checked whether there are any problemsin the signal circuitry such as contacts of the antenna electrodes,grounding of the antenna electrodes. The diagnostic results are sent as“0” if no problems exist and as “1” if problems exist, and the resultsare sent to the SRS process, which will be described later. In stepS206, received detected data ADn is processed with the initial data SDn,to obtain essentially true data DTn, and it is judged whether thepassenger sitting in seat 1 is an adult or a child. In step S207, SRSprocess is carried out between the control circuit 22 and the airbagapparatus (SRS) 30. When step S207 is completed, it returns to step S4and repeats the steps S204 to S206 at certain intervals. Initialdiagnostics in step S203 and circuit diagnostics in step S205 may beintegrated into each other or omitted.

Initial diagnostics in FIG. 16 are carried out as outlined in FIG. 17.First, in step SA201, stored data are sent from the control circuit 22to the control circuit CC in the airbag circuit 30. In step SA202,passenger data are received from the airbag apparatus 30. In step SA203,it is examined whether the received data from the airbag apparatus 30match the stored data. If the data are matched, the process iscontinued. If the data do not match, it is judged that problems exist inthe com circuit and fail-safe process is carried out and warning lamp isturned on, for example. The initial diagnostics may be carried out bysending the stored data from the airbag apparatus 30 to the controlcircuit 22 so that matching process can be carried out in the controlcircuit CC in the airbag apparatus 30.

Signal reception process in FIG. 16 is carried out as outlined in FIG.18. First in step SB201, the control circuit 22 successively selects oneswitching device at a time from the switching devices 18 a˜18 d so thatonly the switching circuit 18 a is closed, for example, to select anantenna electrode 4 a. In step SB202, the data from the respectiveantenna electrode and phase difference are received in the controlcircuit 22. In step SB203, it is examined whether successive selectionof antenna electrodes 4 a˜4 d by the successive actions of the switchingdevices 18 a˜18 d has been completed. If it is judged that the switchingprocess has been completed, it proceeds to passenger evaluation process.If it is judged that the switching process is incomplete, it returns tostep SB201.

The passenger evaluation process is carried out as outlined in FIG. 19.First, in step SC201, based on the initial value SDn read from theexternal memory, the measured signal data related to current flowing inall the antenna electrodes 4 a˜4 d are processed so as to calculate theessentially true data DTn (=SDn−ADn). In step SC202, the true data DTnreceived by the control circuit 22 and the threshold values related topassenger evaluation are compared to decide whether the true data DTnare higher than the threshold values. If the true data DTn are higherthan the threshold values, it proceeds to step SC203, and if it isjudged that the true data are not higher, it proceeds to step SC204. Instep SC203, if it is judged that the passenger sitting on the seat isjudged to be an adult, it proceeds to step SC205, so that ON-data forplacing the airbag apparatus 30 in the deployable state are entered inthe SRS process, and the program connects to SRS process. Also, in stepSC3, if the passenger sitting on the seat is judged to be a child, itproceeds to step SC5, and OFF-data for not deploying the airbagapparatus 30 are entered, and the program is continued.

The SRS process is carried out as outlined in FIG. 19. First, in stepSD201, ON-data for placing the airbag apparatus in the deployable stateor OFF-data for placing the airbag apparatus in the not-deployable stateand system check-data (problem information) are sent from the passengerdetection unit circuitry (control circuit 22) to the airbag apparatuscircuitry (control circuit CC). In step SD202, OK-data or NG-data inresponse to the ON-data and OFF-data from the airbag apparatus circuitryand system check-data are received by the control circuit 22, and itproceeds to step SD203. In step SD203, it is judged whether theON-/OFF-data and system check-data, which had been sent from thepassenger detection unit circuitry to the airbag apparatus circuitry,are returned again from the airbag apparatus circuitry to the passengerdetection circuitry in the normal condition. If it is judged to benormal (no problem in corn circuit), the process is continued. If thereis a problem in the com circuit, it proceeds to step SD204, and it isexamined whether the fail-safe timer is at zero. This detection processof circuit problems is programmed to repeat three times. Therefore, ifit is judged that the fail-safe timer is zero, fail-safe process iscarried out, and a warning lamp is activated, for example. If it isjudged that the fail-safe timer is not at zero, it proceeds to stepSD205, and fail-safe timer count is performed, and the process iscontinued.

On the other hand, in step SE201, the airbag apparatus circuitry(control circuit CC) receives ON-data for placing the airbag apparatusin the deployable state or OFF-data for placing the airbag apparatus inthe not-deployable state and system check-data from the passengerdetection unit circuitry (control circuit 22). In step SE202, thereceived data are checked to examine whether or not they are normal. Ineither case, it proceeds to step SE203. In step SE203, OK-data orNG-data and system check-data are sent to the passenger detection unitcircuitry. If, in step SE202, it is judged that the com circuit isnormal, OK-data are sent in step SE3, and it proceeds to step SE204. Instep SE204, the data on the airbag side is renewed in response toOK-data, thereby placing the airbag in the deployable state ornot-deployable state. If, in step SE202, it is judged that there is aproblem in the corn circuit, NG-data are sent in step SE203, and itproceeds to step SE205. In step SE205, it is examined whether thefail-safe timer is at zero. This detection process of circuit problemsis programmed to repeat three times. Therefore, if it is judged that thefail-safe timer is zero, fail-safe process is carried out, and a warninglamp is activated, for example. If it is judged that the fail-safe timeris not at zero, it proceeds to step SE206, and fail-safe timer count isperformed, and the process is continued.

According to this embodiment, the passenger evaluation process isperformed according to the true data DTn (=SDn−ADn) obtained bysubtracting the measured signal data ADn from the initial data SDn,relating to the reference state such as vacant seat that are stored inexternal memory. Therefore, by initializing each sensor in terms of thereference values of the sensors, it is possible to compensate for thescatter in the results caused by slight characteristic differences inthe installation conditions of the antenna electrodes and fluctuationsin installed components. This process increases the reliability andprecision for the passenger evaluation process.

Also, signal data related to the perturbation current caused byselectively activating the antenna electrodes 4 a˜4 d disposed on theseat 1, are subtraction processed using the initial data SDn stored inthe control circuit 22, and seating conditions including passengerloading are judged on the basis of the corrected data, which is sent tothe airbag apparatus 30, and these series of steps are repeated atcertain intervals, and therefore, deployment of the airbag apparatus 30can be controlled appropriately according to data on passenger loadingand other data.

The beneficial effects of Embodiment 2 are the same as those inEmbodiment 1. It is obvious that Embodiment 2 can be applied to otherembodiment shown in FIG. 15.

Embodiment 3

Next, the passenger detection system in Embodiment 3 will be presentedwith reference to the drawings. The passenger detection system in thisembodiment is based on detecting the perturbation current related topassenger seating conditions more effectively by using an impedancematching circuits and various designs of antenna electrodes. Those partswhich are the same as the parts shown in FIGS. 96˜97 will be given thesame reference numerals and their detailed explanations will be omitted.FIGS. 2, 21 show the arrangement of the passenger seat 1 and the antennaelectrodes, and seat 1 is comprised primarily of a sitting section 1 aand a backrest section 1 b. The sitting section 1 a is comprised by aseat frame 3 fixed to the base 2 which can be moved forward andbackward, and an outer covering for the cushion. Particularly, aplurality of antenna electrodes 304 of substantially the same shape (forexample, rectangular spiral), separated at some distance, are disposedsymmetrically on the sitting section 1 a. The antenna electrodes 304 maybe disposed on the outside the covering or on the outer covering orcushion material itself. A control unit 10 is disposed on or near theseat frame 3.

The antenna electrode 304, as shown in FIG. 21, is basically comprisedof a base member 305 made of an insulator such as non-woven fabric, andantenna electrodes 304 a˜304 d placed separately and symmetrically onone surface of the base member 305, and in spirals using an electricallyconductive material having a line or strip shape, and are disposed onthe inside of the outer covering member. The antenna electrodes 304a˜304 d have an internal space section G bounded by peripheries andwhere there is no electrode, and it is preferred that the electrodes beformed on an electrically conductive cloth. The antenna electrode 304a˜304 d may be made of fine metallic wire, or a conductive fiber woveninto the base member 305, or screen printing, coating or spraying ofelectrically conductive material containing copper powder, graphitepowder or silver powder on the base member 305. Or, the outer coveringfor the sitting section 1 a or cushion may be used as base member and aconductive material may be screed printed, coated or sprayed using ametallic wire, or an electrically conductive fiber may be woven in thefabric. They may also be fabricated into spiral shapes by etching a thinflexible metallic strip or etching an electrically conductive flexiblethin material made by vapor depositing or electroplating an electricallyconductive material on an insulator.

Especially, when the antenna electrodes 304 a˜304 d are made ofelectrically conductive material, or a electrically conductive materialin a line or strip shape, the antenna electrodes may be adhesivelybonded or bonded using a thermoplastic or thermosetting material,sewing, hooking, button, hooks, or adhesive tape. Adhesive bonding ispreferred. The antenna electrodes 304 a˜304 d shown in the drawing areformed into rectangle spirals of substantially the same size. Theantenna electrode section 304 contain many antenna electrodes 304 a˜304d but they are essentially synonymous functionally and are usedinterchangeably in the following presentation.

The antenna electrode 304 is constructed as shown in FIGS. 21A, 21B. Alead wire 306 (306 a˜306 d) including shielding wire makes anelectrical/mechanical connection on one end of the antenna electrodes304 a˜304 d using pressure clamps (bonding means) 307, and the lead wire306 (306 a˜306 d) is attached to a connector 308 at the output end, andis connected to the connectors (19 a˜19 d) of the control unit 10.Particularly, when the antenna electrodes 306 a˜306 d are to be made ofmetallic wire, lead wire (306 a) and the antenna electrode wire (304 a)may be made of the same wire.

In this embodiment, a plurality of antenna electrodes 304 a˜304 dprovided in the seat 1 have a space G bounded by the peripheries of theantenna electrode section where there is no conductive material of theantenna electrodes. Therefore, the wire material is reduced and the costis lowered. Especially, when the antenna electrode section is made of anelectrically conductive woven material, reduction in the material usagemeans lower cost.

Also, The antenna electrodes 306 a˜306 d are provided with as manyspaces G as possible without causing problems in use, so that thecushioning of seat 1 is not affected. Therefore, seating comfort levelis maintained.

Particularly, when the space G is in the center of the antenna electrodesection, there is hardly any effect on the performance of the antennaelectrodes, but when the spaces G of very large size are located nearthe peripheral regions, the performance may be affected to some extentby lowering the perturbation current in the antenna electrodes. Theshapes shown in these drawings are those that have the least effect onthe performance of the antenna electrodes.

Also, the overall antenna electrode section is made by bonding aplurality of antenna electrodes 304 a˜304 d on an insulating base member305, it is possible to secure the spacing and arrangement of the antennaelectrodes simply by positioning the base between the outer covering andthe cushion material, without having to made any adjustment operations.After installing the section 306, there is no problem of shifting of theantenna electrodes 304 a˜304 d. Therefore, information obtained from theperturbation current is reliable and the precision of passenger seatingevaluation is improved.

When the antenna electrodes 304 a˜304 d are placed individually betweenthe outer covering and the cushion material, without using the basemember 305, the spacing between the electrodes must be laboriouslyadjusted individually, and further more, there is a problem of shiftingof the antenna electrodes caused by the use, and the reliability ofinformation can suffer.

Also, lead wires 306 a˜306 d are extended from the antenna electrodes304 a˜304 d, therefore, connections to the control unit 10 arefacilitated. Specially, if connectors 308 are provided on the ends ofthe lead wires, connections to the control unit 10 is facilitated evenmore.

Also, the pressure terminals 7 are used to clamp the antenna electrodes304 a˜304 d with the lead wires 306 a˜306 d so that the electricalconnections can be provided reliably.

FIG. 22 shows another example of the antenna electrode. It is similar tothe antenna electrode shown in FIG. 21, but the difference is that aninsulating cover member 305A is used to guard an integral unit includingthe base member 305 and the antenna electrodes 304 a˜304 d. It ispreferred that the members be bonded using a an adhesive, thermoplasticor thermosetting resin. When using the thermoplastic or thermosettingresin, it is preferable to bond to the base member 305 and/or covermember 305A.

In this embodiment, the antenna electrodes 304 a˜304 d are protected bythe base member 305 and the cover member 305A, damage to the unit duringassembly is minimized to improve productivity. Furthermore, because ofthe provision of spaces G, although the support strength for the basemember 305A is reduced, unitizing of the base member 305 with the covermember 305A by clamping improves the strength to a level that will beacceptable for practical purposes.

FIG. 23 shows another example of the antenna electrode, which isbasically the same as that shown in FIG. 21, but the difference is thata plurality of snaking antenna electrodes (304 a˜304 d) are disposed onone surface of the base member 305. The snaking antenna electrodes 304a˜304 d are interspaced with spaces G.

FIG. 24 shows another example of the antenna electrode, which isbasically the same as that shown in FIG. 21, but the difference is thata rectangle shaped spiral antenna electrode 304 a is formed on onecorner of a flexible substrate member 340, and fixed to the base member305. At the end of the antenna electrode 304 a, a substantially circularconductive land 341 having a center hole 342 is provided, and thesubstrate member 340 is bonded to the base member 305. A lead wire 306 ais attached to the conductive land 341 using a terminal lug 344 clampedby a pressure terminal 307 by fastening means 343 such as riveting toclamp the terminal lug 344, conductive land 341, flexible substrate 340and the base member 305 in the center hole 342. The same arrangementsare made for other antenna electrodes 304 b˜304 d.

This type of antenna electrode 304 a is made by deposing metals such ascopper, aluminum or nickel to made a thin film on the entire surface ofa flexible substrate 340 using electroplating, vapor deposition orinjection molding, and by etching the film to form the electrodes. It isalso possible to carry out deposition and fabrication processconcurrently by using making on the surface during the depositionprocess to form the electrode section. It is also possible to form theelectrode section by screen printing using a conductive paste.

According to this embodiment, mass production of antenna electrodes ofuniform quality can be produced, thereby increasing the reliabilitypassenger detection system and lowering the cost of production.

FIG. 25 shows another example of the antenna electrode, which isbasically the same as that shown in FIG. 21, but the difference is thata plurality of antenna electrodes 304 a (304 b˜304 d) are provided onone surface of the base member 305 to form a comb structure usingconductive wire or strip, which is fixed to the base member 305. Thecomb-shaped antenna electrode 304 a is provided with interspaced spacesG. The comb sections may be provided on both sides.

In this embodiment, the shape of the antenna electrode 304 a (304 b˜304d) is simple so that fabrication is relatively easy and passengercomfort can also be assured.

FIG. 26 shows another example of the antenna electrode, which isbasically the same as that shown in FIG. 21 but the difference is thatthe electrode is loop shaped, and the inside space G is surrounded bythe antenna electrode wire. Such an antenna electrode is place at fourcorners of the base member 305.

This example further reduces the number of parts required to make theantenna electrode section, and the manufacturing cost can besignificantly lowered.

FIG. 27 shows another example of the antenna electrode, which isbasically the same as that shown in FIG. 21 but the difference is thatthe shape of the antenna electrode 304 a is substantially a rectangleframe and the inside space G is surrounded by tape conductor.

The antenna electrode section is fabricated by forming the space G isvarious ways such as cutting a space G in the center section of aconductive cloth, punching or etching a space G in the center section ofa metal strip, or forming the space G on base member 305 by screenprinting, coating, spraying, molten metal injection. When the antennaelectrode section and the base member 305 are made separately, they canbe united by adhesive bonding, bonding with thermoplastic orthermosetting resin, sewing, or by attaching with mechanical fasteners.

FIG. 28 shows a block diagram of another example of the circuitconfiguration, which is basically the same as that shown in FIG. 5, butthe difference is that the amplitude control circuit 12 is omitted, andthe direct measuring type electric current detection circuit(information detection circuit) 15 is replaced with an indirectmeasuring type information detection circuit 315A for obtaininginformation regarding electric current flow in the antenna electrodesindirectly. The singular power source Vcc generated in the electricpower circuit 324 is a constituting element for the control unit 310,and is supplied to all the elements requiring power source Vcc (electricfield generation device 311, information detection circuit 315A,switching circuit 318, control circuit 322, communication interface 326and others).

The information detection circuit 315A is comprised by: an impedanceconversion section 315Aa (operational amplifier of amplificationfactor 1) connected to the output line from the electric fieldgeneration device 311 and an ac-dc conversion section (smoothing device)having a resistor 315Ab connected to the output side of the impedanceconversion device 315A and a condenser 315Ac. By inserting the impedanceconversion section 315Aa, the impedance in the input side is increasedwhile, in the output side, the impedance is lowered. Therefore, thecurrent level required by the control circuit 322 for accessing data canbe obtained without affecting the performance of the forward signals inthe output signal line. The impedance conversion section 315Aa may beomitted depending on the detection content and detection precisionrequired by the system.

Also, the electric field generation device 311 is comprised by aresistor 311 a and a switching device 311 b operated by field-effecttype transistors which is turned on/off by a trigger signal from thecontrol circuit 322, and HFLV signals are output from the drain. If Vccis a 5 volt dc, rectangular waveform having an amplitude of 5 volts isgenerated.

The operation of the passenger detection system is as follows. First,the electric field generation device 311 is controlled by a triggersignal sent from the control circuit 311 to the switching device 311 b,which undergoes on/off actions, and when the switching device is off,HFLV signals having a rectangle shape is output. The output signal isimpressed on the antenna electrode section (304 a˜304 d) through theswitching circuit 318 and a weak electric field is generated in itsvicinity. When a passenger is sitting on the seat 1, a perturbationcurrent, dependent on the strength of the electric field, flows in theantenna electrode section (304 a˜304 d) through the resistor 311 a ofthe electric field generation device 311 and the switching circuit 318.In this case, the leading portion of the rectangular waveform is roundeddepending on the RC time constant affected by the passenger portion ofthe capacitance effect and the resistance 311 a. The rounded rectangularoutput waveform is received in the ac-dc conversion section through theimpedance conversion section 315Aa, and is converted to a dc signal andreceived in the control circuit 322. When the seat 1 is vacant, there islittle current flowing from the electric field generation device 311 tothe antenna electrode section so that dc output from the informationdetection circuit 315A becomes higher compared to when the passenger issitting on seat 1. However, threshold values intermediate between thetwo levels are stored in the control circuit 322, therefore, bycomparing the signal data received in the control circuit 322 with thethreshold values, passenger seating condition can be decided. The resultobtained by the control circuit 322 is sent to the airbag apparatus 30through the communication interface 326, and the airbag is made eitherdeployable or not-deployable.

In this embodiment, HFLV signals are output from the electric fieldgeneration device 311, and the output line is connected to the ac-dcconversion section through the impedance conversion section 315Aa,therefore, the voltage information (voltage waveform) of theperturbation current flowing in the antenna electrodes 304 a˜304 d canbe converted to a dc signal, and the passenger seating conditions can bejudged accordingly.

Also, because the input side has a high impedance while the output sidehas a low impedance by having an impedance conversion section 315Aabetween the output line and the ac-dc conversion sections (315Ab,315Ac), when the control circuit 22 consumes the dc output current fromthe ac-dc conversion section (smoothing circuit), forward signals in theoutput line are hardly affected when the current is consumed in thecontrol circuit 22 for evaluating the data. This effect contributes tohigher precision in passenger detection.

Also, the electric power circuit 324 as an element in the control unit310 produces a singular power source Vcc by adjusting the voltage formthe battery power BA to singular dc voltage so that all the elements inthe control unit 31A requiring the electrical power will be served bythe same constant voltage Vcc, therefore, the electric circuit can beconstructed using a three-terminal regulator to simplify the circuit,and together with simplifying the structure of the antenna electrodesection, the system is simplified and the system cost is lowered.

Specially, if one of the antenna electrode section is placed on thedashboard or door or sideport of the seat, when a child sitting in thepassenger seat, for example, it is possible to detect a space betweenthe passenger and the dashboard or door so that even if the spacebetween the passenger and the dashboard or door becomes narrower thannormal because of the position of the passenger or other factors, theairbag apparatus can be operated properly. Therefore, by using thissystem with the system shown in FIG. 28, the passenger detection systemcan be made more finely responsive. This system can be used inconjunction with the example shown in FIG. 5 or by itself.

It should be noted that the present invention is not limited by theexamples given above, and for example, the number of antenna electrodes(antenna electrode section) can be adjusted suitably, and the electrodeshape can be changed to loop shapes including angular spiral, circularloop, honeycomb shape, and the antenna electrode section can be made bymaking a laminated material of angular, circular, rectangular shape madeof metal plate or electroplating, vapor deposition, or screen printing,and forming a plurality of spaces of angular or round shapes. Theelectric field generation device can be produced by suitably dividingthe clock signals in the control circuit, and output frequency can beselected other than 120 KHz to suit the condition inside the car, andthe voltage can be selected to be outside of the 5˜12 volt range. Also,the amplitude control circuit, phase shift detection circuit may beomitted if the system requirements do not warrant such devices. Also,the judging result of the control circuit can be applied to control ofthe seat belt use and warning light, for example. Further, passengerevaluation can be based on pre-stored reference data on seating patternof the passenger on the seat and sitting posture, and comparing thedetected data with the reference data to obtain information on passengerloading and passenger identity.

Embodiment 4

Embodiment 4 of the passenger detection system will be presented withreference to FIGS. 29˜32. The passenger detection system in thisembodiment is based on detecting the perturbation current related topassenger seating conditions by means of an ac-dc conversion process,and signal interference effects are prevented by applying a dc potentialto all non-active antenna electrodes. Those parts of the system that arethe same as those shown in FIGS. 96, 97 are given the same referencenumerals, and their explanations are omitted. FIGS. 29˜32 show variouspassenger seats, where the seat 401 is primarily comprised by a sittingsection 401 a and the backrest section 1 b. The sitting section 401 a iscomprised by: a seat frame section 403 fixed to a base 402 that isslidable forward and backward; cushion member disposed above the seatframe 403; and outer covering, and the backrest section 401 b iscomprised by a cushion member placed on the front of the seat frame; andouter covering for the cushion. Particularly, the sitting section 1 ahas a plurality of separate antenna electrodes 404 (404 a˜404 b), andthe backrest section 1 b has a plurality of separate antenna electrodes404 (404 c˜404 d). The antenna electrode 404 may be placed on theoutside or on the cushion member itself. A control unit 410 is disposedon or near the seat frame.

The antenna electrode 404 is made of a conductive cloth, but metallicthreads may be woven into the seat fabric on the sitting section 401 aand the backrest section 401 b, or applying a conductive paint on thecloth, or using metal strips. It is preferable that the antennaelectrode 404 be comprised by unitizing a plurality of antennaelectrodes 404 a˜404 b, 404 c˜404 d of a uniform size (width 70 mm andlength 400 mm, for example) separated at a given distance (50 mm, forexample) on one surface of the base members 405 made of an insulatingmaterial, as shown in FIG. 30, and on the inside of the sitting section401 a and the backrest section 401 b. Lead wires 406 (406 a˜406 d)including shield wires are independently extended from the antennaelectrodes 404 a˜404 d, and are connected to the connectors (orterminals) 419 a˜419 d of the control unit 410.

The control unit 410, disposed on the seat frame 403 or its vicinity, iscomprised by, as shown in FIG. 31: an electric field generation device(oscillator and the like) 411 for generating a weak electric fieldaround the antenna electrode 404 by HFLV signals of 5˜12 volts and afrequency at approximately 100 KHz; an amplitude control circuit 412 forcontrolling the amplitude of the forward signal from the oscillationcircuit 411 approximately constant; a current detection circuit 415 fordetecting the forward current signal; an ac-dc conversion circuit 416for converting the output signal in the current detection circuit 415 todc; an amplifier 417 for amplifying the output signal from the ac-dcconversion circuit 416; a switching circuit 418 having a plurality ofswitching devices 418 a˜418 d for the antenna electrodes 418 a˜418 d,connected to the current detection circuit 415; connectors 419 a˜419 ddisposed in the housing of the control unit, connected to the switchingdevices 418 a˜418 d of the switching circuit 418; a control circuit 420including MPU and the like; connector 421 connected to the batterysource (not shown) disposed in the housing; and an electric powercircuit 422 connected between the connector 421 and the control circuit420. In the switching circuit 418, one terminal a in the switchingdevise 418 a˜418 d is connected to the current detection circuit 415,and the other terminal b is connected to the electric power circuit 422,and the other terminal b are impressed with a dc voltage of about 5volts from the electric power circuit 422. The control circuit 420 isconnected to such an airbag apparatus 430 as shown in FIG. 32. Selectiveswitching of the terminals a, b of the switching devices 418 a˜418 d isperformed according to the signal from the control circuit 420.

In the control unit 410, the amplitude control circuit 412 includes anamplitude varying circuit 413 for varying the voltage amplitude of theforward signals, and amplitude detection circuit 414 for detecting thevoltage amplitude of the forward signals. The amplitude varying circuit413 is comprised by an amplitude varying section 413 a including aprogrammable gain amplifier (PGA) and others, and the amplitudedetection circuit 414 is comprised by: a voltage amplitude detectionsection 414 a having an op-amp; an ac-dc conversion circuit 414 b forconverting the output signal from the amplitude detection circuit 414 ato dc; and an amplifier 414 c for amplifying the output signal from theac-dc conversion circuit 414 b. Output signal from the amplifier 414 cis supplied to the control circuit 420, and the amplitude varying signalfor the amplitude varying section 413 a is generated by the controlcircuit 420.

In the control unit 410, the current detection circuit 415 includes animpedance element, for example resistor 415 a, connected in series tothe signal circuit (forward signal side) and an amplifier 415 b, such asdifferential amplifier, for amplifying the terminal voltage of theresistor 415 a. The output side of the current detection circuit 415 isconnected to the control circuit 420 through the ac-dc conversioncircuit 416 and the amplifier 417. The output side of the resistor 415 ain the current detection circuit 415 is connected to the connectors 419a˜419 d through the switching circuit 418 (terminal a, switching devices418 a˜418 b).

The passenger detection system having the above structure operates inthe following manner. First, the oscillation circuit 411 generates HFLVsignals whose voltage amplitude is detected by the detection section 414a of the amplitude detection circuit 414, and the detection signal isconverted to a dc signal in the ac-dc conversion circuit 414 b, and theamplified signal from the amplifier 414 c is input in the controlcircuit 420. The control circuit 420 evaluates whether the detectedvoltage amplitude meets the required amplitude value, and sends theamplified signal to the amplitude varying section 413 a to correct theamplitude to the required value. This process controls the voltageamplitude of the forward signal to a given voltage amplitude, andhenceforth, voltage amplitude of the forward signal is corrected to agiven amplitude value by the linking action of the amplitude varyingcircuit 413 and the amplitude detection circuit 414.

The forward signal having a constant voltage amplitude is impressed onantenna electrode 404 through the current detection circuit 415,switching circuit 418, connectors 419 a˜419 d, resulting in thegeneration of weak electric fields in the vicinity of the antennaelectrode 404. In this process, switching circuits 418 are operated bysignals from the control circuit 420 so that, first, only the switchingdevice 418 a is connected to terminal a, next only the switching device418 b is connected to terminal b, and such a stepwise switching issuccessively carried out so that when a particular switch contacts thecorresponding terminal a, other switches are all contacted with terminalb so that dc voltage is provided. Therefore, when the particularswitching device contact the respective terminal a, constant-amplitudeforward signal passes through the current detection circuit 415, theparticular switching device, the particular connector and reaches theparticular antenna electrode (404 a˜404 d), generating an electric fieldin the vicinity of the particular antenna electrode, so that differentvalue of the perturbation current, governed by the passenger seatingconditions (passenger loading, passenger posture on seat 401, passengeridentity), flows in the antennae circuit. The current is detected by thecurrent detection circuit 415, converted to dc in the ac-dc conversioncircuit 416, amplified in the amplifying circuit 417 and aresuccessively input in the control circuit 420.

In the control circuit 420, threshold values (threshold data) regardingpassenger seating conditions (loading, seating posture and identity) arealready stored. For example, the current level flowing in the electrodesis higher when a passenger is sitting on the seat, therefore, thereference can be based on whether the perturbation current data exceedsa given constant value. However perturbation currents flowing in variousantenna electrodes will have certain characteristic patterns, so thatsuch patterns may be utilized for evaluation. Also, regarding passengerposture and passenger identity, characteristic value of current flows inelectrodes depending on the passenger posture and passenger identity, sothat the reference can be based on such characteristic values, as wellas the current patterns.

Therefore, the detected data received in the control circuit 420regarding the current values flowing in the antenna electrodes 404 a˜404d are subjected to various computation processes. For example, detecteddata are compared against the threshold values in stored data regardingpassenger loading and passenger identity to determine whether thepassenger is an adult or a child. Based on such result, the airbagapparatus 430 is made, by the command signal from the control circuit420, to be deployable or not-deployable. Specifically, the airbagapparatus 430 is programmed such that the signal from the controlcircuit 420 is input in the control circuit CC does not supply a gatesignal to the switching element SW2 when the passenger is a child, butsupplies a gate signal to the switching element SW2 when the passengeris an adult. Therefore, when an accident occurs, the airbag is notdeployed when the passenger is a child while the airbag is deployed whenthe passenger is an adult. The driver side airbag is deployed regardlessof the conditions in the passenger side.

Next, the process of operation of the passenger detection system will beexplained with reference to the overall flowchart shown in FIG. 33.FIGS. 34˜37 shows steps in sub-processes. First, as shown in FIG. 33,the ignition circuit is turned on so that the process is in START. Instep S401, the program is initialized, and proceeds to step S402. Instep S402, initial diagnostics are performed for communication betweenthe control circuit 420 and the airbag apparatus 430. In step S403, itexamines whether the engine is operating, and if it is judged that theengine is operating, it proceeds to step S404. If it is judged that theengine is not operating, the program is shutoff. In step S404, signaldata related to the perturbation current flowing in a particular antennaelectrode, resulting from impressing a weak electric field on theparticular antenna electrodes 404 a˜440 d, are received in the controlcircuit 420. In step S405, based on the received data, passenger loadingdata, passenger identity data are examined and conclusions reached. Instep S406, SRS process is carried out between the control circuit 420and the airbag apparatus (SRS) 430. When step S406 is completed, itreturns to step S404 and repeats the steps S404 to S406. Step S403 maybe omitted.

Initial diagnostics are carried out as outlined in FIG. 34. First, instep SA401, stored data are sent from the control circuit 420 to thecontrol circuit CC in the airbag circuit 30. In step SA402, passengerdata are received from the airbag apparatus 430. In step SA403, it isexamined whether the received data from the airbag apparatus 430 matchthe stored data. If it is judged that the data are matched, the processis continued. If the data do not match, it is judged that problems existin the com circuit and fail-safe process is carried out and alert lampis turned on, for example. The initial diagnostics may be carried out bysending the stored data from the airbag apparatus 30 to the controlcircuit 420 so that matching process can be carried out in the controlcircuit CC in the airbag apparatus 430.

Signal reception process is carried out as outlined in FIG. 35. First instep SB401, the control circuit 420 successively selects a particularswitching device at a time from the switching devices 418 a˜418 d sothat only the switching circuit 418 a contacts its terminal a, next,only the switching device 418 b contacts its terminal a, and so on toactivate respective antenna electrode (404 a˜404 d). During thisprocess, all switching devices other than the particular selected deviceare connected to the respective terminal b, and are impressed with a dcvoltage signal. In step SB402, current data flowing in successiveantenna electrodes 418 a˜418 d are received in the control circuit 420,and it proceeds to step SB403. In step SB403, it is examined whethersuccessive selection of antenna electrodes 404 a˜404 d caused bysuccessive actions of switching devices 418 a˜418 d contactingrespective terminals a and b has been completed. If it is judged thatthe switching process has been completed, it proceeds to passengerevaluation process. If it is judged that the switching process isincomplete, it returns to step SB401.

The passenger evaluation process is carried out as outlined in FIG. 36.First, in step SC401, it is judged whether or not a sum of successivedata on the current levels flowing in all the antenna electrodes 404a˜404 d is larger than the threshold value THe. If the measured signaldata are higher than the threshold value THe, it proceeds to step SC402on the basis that a passenger is sitting on the seat 1, and if it isjudged that the signal data are not higher, it proceeds to step SC404.In step SC402, it is judged whether the passenger sitting on the seat isan adult or a child, and if the judgment is an adult, it proceeds tostep SC403, and if the judgment is a child, it proceeds to step S404. Instep S404, because the passenger is an adult, ON-data for placing theairbag apparatus 430 in the deployable state are entered in the SRSprocess, and the program connects to SRS process. Also, in step SC404,because the passenger sitting on the seat is a child (or vacant),OFF-data for not deploying the airbag apparatus 430 are entered in theSRS process, and the program is continued. If the seat is vacant, it maybe programmed to proceed to step S403.

The SRS process in FIG. 33 is carried out as outlined in FIG. 37. First,in step SD401, ON-data for placing the airbag apparatus in thedeployable state or OFF-data for placing the airbag apparatus in thenot-deployable state and system check-data are sent from the passengerdetection unit circuitry (control circuit 420) to the airbag apparatuscircuitry (control circuit CC). In step SD402, OK-data or NG-data inresponse to the ON-data and OFF-data and system check-data from theairbag apparatus 430 are received in the control circuit 420, and itproceeds to step SD403. In step SD403, it is judged whether theON-/OFF-data and system check-data, sent from the passenger detectionside to the airbag apparatus circuitry, are again returned from theairbag apparatus circuitry to the passenger detection side in the normalcondition. If it is judged to be normal (no problem in signal circuit),the process is continued. If there is a problem in the com circuit, itproceeds to step SD4, and it is examined whether the fail-safe timer isat zero. This detection process of circuit problems is programmed torepeat three times. Therefore, if it is judged that the fail-safe timeris zero, fail-safe process is carried out, and a warning lamp isactivated, for example. If it is judged that the fail-safe timer is notat zero, it proceeds to step SD405, and fail-safe timer count isperformed, and the process is continued.

On the other hand, in step SE401, the airbag apparatus circuitry(control circuit CC) receives ON-data for placing the airbag apparatusin the deployable state or OFF-data for placing the airbag apparatus inthe not-deployable state and system check-data from the passengerdetection unit circuitry (control circuit 420). In step SE402, thereceived data are checked to examine whether or not they are normal. Ineither case, it proceeds to step SE403. In step SE403, OK-data orNG-data and system check-data are sent to the passenger detection unitcircuitry. If it is judged, in step SE402, that the signal circuit isnormal, OK-data are sent in step SE403, and it proceeds to step SE404.In step SE404, the data on the airbag side is renewed in response to theOK-data, thereby placing the airbag in the deployable state ornot-deployable state. If it is judged, in step SE402, that there is aproblem in the corn circuit, NG-data are sent to the control circuit 420in step SE403, and it proceeds to step SE405. In step SE405, it isexamined whether the fail-safe timer is at zero. This detection processof circuit problems is programmed to repeat three times. Therefore, ifit is judged that the fail-safe timer is zero, fail-safe process iscarried out, and a warning lamp is activated, for example. If it isjudged that the fail-safe timer is not at zero, it proceeds to stepSE406, and fail-safe timer count is performed, and the process iscontinued.

According to this embodiment, a plurality of antenna electrodes 4 (4 a˜4d) are disposed in the sitting section 401 a and/or the backrest section401 b separately, and weak electric fields are generated successivelyaround each electrode and the resulting signal data related to theperturbation current flowing in the antenna electrodes are processed tocarry out the passenger detection process. However, one antennaelectrode at a time is activated and all other antenna electrodes areimpressed with a dc voltage so that external signal interference can beavoided because of lesser interference effects. This approach isadvantageous because of the stability of the electric field generated,and consequently, the perturbation current measurement is also stable.Therefore, by detecting the values of such perturbation current, it ispossible to detect readily whether the seat is vacant or the passengeris an adult or a child, thereby improving the detection precision.Especially, the circuitry allows selection of setting the airbagapparatus 430 to be either in the deployable state or not-deployablestate so that unwanted airbag deployment can be prevented.

Especially, the control circuit can be designed so that a dc voltage(applied to all the antenna electrodes not generating an electric field)is generated by the electric power circuit 422, and sharing the samevoltage (5 volts for example) with the oscillation circuit 411 andcontrol circuit 420 enables to avoid having a separate power source forthe dc voltage to stabilize the electric field generation process at lowcost. It is also possible to connect to a ground potential instead of dcvoltage (dc potential) to stabilize the electric field generation.

Also, because a plurality of antenna electrodes 404 a˜404 d can beselectively switched to the oscillation circuit 411 and a dc voltagesource (422) by the switching action of the switching device 814 bysignals from the control circuit 420, contact to terminals a and b ofthe switching devices 814 a˜814 d can be performed quickly andaccurately. Thus, the perturbation current flowing in a particularantenna electrode can be detected precisely by the current detectioncircuit 415, and signal data regarding the perturbation current arereceived accurately in the control circuit 420.

FIG. 38 shows a plan view of another example of the seat 401, having asitting section 401 a with a plurality of antenna electrodes 404 a˜404 ddisposed symmetrically on front/rear and left/right sections, but thebackrest section 401 b is not provided with any antenna electrode. Thecontrol unit to provide selective switching of the antenna electrodes,electric fields and dc voltage (or grounding) is basically the same asthat shown in FIG. 31.

In this example, because a pattern of perturbation current in theantenna electrodes (404 a˜404 d) produced by the sitting passengercorresponds to a sitting posture of the passenger, it can accuratelyjudge whether or not the sitting posture is normal without muchinterference from external noise.

FIG. 39 shows a front view of another example of the seat 401, having abackrest section 401 b with a plurality of antenna electrodes 404 a˜404d disposed symmetrically on top/bottom and left/right sections, but thesitting section 401 a is not provided with any antenna electrode. Thecontrol unit to provide selective switching of the antenna electrodes,electric fields and dc voltage (or grounding) is basically the same asthat shown in FIG. 31.

In this example, because a pattern of perturbation current in theantenna electrodes (404 a˜404 d) produced by the sitting passengercorresponds to opposing areas (opposing pattern) of the passengerleaning against the antenna electrodes 404 a˜404 d, it can accuratelyjudge whether or not the sitting posture is normal without muchinterference from external noise.

It should be noted that the present invention is not limited by theexamples given above, and for example, the number of antenna electrodesfor the seat can be adjusted suitably. Electric fields can be producedby switching according to pulse signals from the control circuit, sothat the use of a positive power source only can produce HFLV signals,at output frequencies of the order of 100 KHz to suit the conditioninside the car, and the voltage can be selected to be outside of the5˜12 volt range. Also, the amplitude control circuit may be omitted ifthe system requirements do not warrant such devices. Also, the judgingresult of the control circuit can be applied to control of the seat beltuse and warning light, for example.

Embodiment 5

Next, the passenger detection system in Embodiment 5 will be presentedwith reference to FIGS. 40˜46. The passenger detection system in thisembodiment is based on detecting the perturbation current related topassenger seating conditions by using improved phase shift detectionenabled by a waveforming technique. Those parts which are the same asthe parts shown in FIGS. 96˜97 will be given the same reference numeralsand their detailed explanations will be omitted. FIGS. 40˜42 show thearrangement of the passenger seat (driver seat) 501 and the antennaelectrodes, and seat 501 is comprised primarily of a sitting section 501a and a backrest section 501 b. The sitting section 501 a is comprisedby a seat frame 503 fixed to the base 502 which can be moved forward andbackward, and an outer covering for the cushion. Particularly, aplurality of antenna electrodes 504 (504 a˜504 d) of substantially thesame shape (for example, rectangle), separated at some distance, aredisposed symmetrically on the sitting section 501 a. The antennaelectrode section 504 may be disposed on the outside the covering or onthe outer covering or cushion material itself. A control unit 510 isassembled into the seat 501, and is disposed on the seat frame 501 orits vicinity.

The antenna electrode section 504 shown in FIG. 41 is basicallycomprised of a base member 505 made of an insulator such as non-wovenfabric, and antenna electrodes 504 a˜504 d placed separately andsymmetrically on one surface of the base member 505, and are placed onthe inside of the covering for the sitting section 501 a. The antennaelectrodes 504 a˜504 d are made of an electrically conductive fabric,but they made be made by: weaving fine metallic wire, or a conductivefiber into the base member 505 or into the seat cloth for the sittingsection 501 a, which may be regarded as the base member; or applying acoating using a conductive paint; or using a thin flexible metallicstrip. The antenna electrodes 504 a˜504 d to the base member 505 may beadhesively bonded or bonded using a thermoplastic or thermosettingmaterial, sewing, hooking, button, hooks, or adhesive tape, but adhesivebonding is preferred. The antenna electrodes 504 a˜504 d shown in thedrawing are formed into rectangles of substantially the same size. Theantenna electrode section 504 contain many antenna electrodes 504 a˜504d but they are essentially synonymous functionally and are usedinterchangeably in the following presentation.

The antenna electrode section 504 is constructed as shown in FIGS. 41A,41B. A lead wire 506 (506 a˜506 d) including shielding wire makes anelectrical connection on one end of the antenna electrodes 504 a˜504 dusing a connection terminal 507, and a terminal lug 507A, and the leadwire 506 (506 a˜506 d) is attached to a connector 509 at the output end,and is connected to the connectors (or terminals) 519 a˜519 d of thecontrol unit 10. Particularly, the connection terminal 507 clampsantenna electrode with a metallic terminal to provide electricalconduction, and brass rivets, hooks can be used.

In the above antenna electrode section 504, the connection structurebetween the antenna electrodes 504 a˜504 d and the lead wire 506 (506a˜506 d) are all essential the same, therefore, explanation will bebased on connecting an antenna electrode 504 a to a lead wire 506 a. Theconnection terminal 507 is riveted through the antenna electrode 504 aand the base member 505. A connection terminal 607 is placed in the ahole provided through the antenna electrode 604 a and the base member605, and a riveting terminal lug 607A is inserted in the connectionterminal 607 prior to riveting, and when the assembly is riveted, itmakes an electrical connection between the terminal lug 607A and theantenna electrode 604 a through the connection terminal 607. Theterminal lug 507A is connected so as to make an electrical/mechanicalcontact with the lead wire 506 a using a fastening means such aspressure lug 508.

The connection between the antenna electrode 504 a and the lead wire 506a may be made as shown in FIG. 41C and FIG. 43. In the former case, anextension member 504 aa is formed at a portion of the antenna electrode504 a, and the extension member 504 aa is connected to the connectionterminal 507. The latter case, one edge of the antenna electrode 504 ais folded to the back side of the base member 505, and the foldbacksection 504 ab, back side antenna electrode 504 a, base member 505 arejoined through a common hole by riveting a connection terminal 507.Also, terminal lug 507A is inserted in the connection terminal 507 priorto riveting.

The control unit 510 is assembled into the seat 501, and the controlunit 501 is comprised by, as shown in FIG. 43, an electric fieldgeneration device (oscillator for example) 511 for generating a weakelectric field in the vicinity of the antenna electrodes 504 a˜504 d; anamplitude control circuit 512 for controlling the amplitude of theforward signal from the oscillation circuit 511 to antenna electrode 504approximately constant; an information detection circuit (currentdetection circuit for example) 515 for detecting current information onthe forward signal; an ac-dc conversion circuit 516 for converting theoutput signal in the current detection circuit 515 to a dc signal; anamplifier 517 for amplifying the output signal from the ac-dc conversioncircuit; a switching circuit 518 connected to the current detectioncircuit 515 and having a plurality of switching devices 518 a˜518 d forthe antenna electrodes 504 a˜504 d; connectors 519 a˜519 d disposed inthe housing of the control unit and connecting to the switching devices518 a˜518 d of the switching circuit 518 during the switching action; aphase shift detection circuit 520 connected to the amplitude controlcircuitry (oscillation circuit side) and the switching circuitry(antenna electrode side) of the current detection circuit 515, fordetecting the phase difference between the forward signal from theoscillation circuit and the application signal to the antennaelectrodes; an amplifier 521 for amplifying the output signal of thephase shift detection circuit 520; a control circuit 522 including CPUand the like; a connector 523 connected to the battery source (notshown) disposed in the housing; and an electric power circuit 524connected between the connector 523 and the control circuit 522 andothers. These components are contained in the same housing for thecontrol unit 510, which is fixed to the seat frame 503 so as not to beexposed. An the airbag apparatus 530, shown in FIG. 46 for example, isconnected to the control circuit 522 in the control unit 510. Selectiveswitching of the switching devices 518 a˜518 d is carried out accordingto the output signals from the control circuit 522.

In this control unit 510, the oscillation circuit 511 is comprised by aseries connected resistor 511 a and switching device 511 b in a dc lineof a constant dc voltage (+Vcc) operated by switching device(field-effect type transistors) 511 b which is turned on/off by atrigger signal from the control circuit 522, and HFLV signals of arectangular waveform are output from the drain to the amplitude controlcircuit 512. The HFLV signals are affected by the trigger signalgenerated by the control circuit 522, and is designed to output atsubstantially 120 KHz. The high frequency signal to the amplitudecontrol circuit 512 is output when the field effect transistor 511 isoff.

The amplitude control circuit 52 in the control unit 510 includes anamplitude varying circuit 513 for varying the voltage amplitude of theforward signals, and amplitude detection circuit 514 for detecting thevoltage amplitude of the forward signals. The amplitude varying circuit513 is comprised by an amplitude varying section 513 a including aprogrammable gain amplifier (PGA) and others, and the amplitudedetection circuit 514 is comprised by: a voltage amplitude detectionsection 514 a having an op-amp; an ac-dc conversion circuit 514 b forconverting the output signal from the amplitude detection circuit 514 ato dc; and an amplifier for amplifying the output signal from the ac-dcconversion circuit 514 b. Output signal from the amplifier 514 c issupplied to the control circuit 522, and the amplitude varying signalfor the amplitude varying section 513 a is output from the controlcircuit 522.

The current detection circuit 515 in the control unit 510 includes animpedance element, for example resistor 515 a, connected in series tothe signal circuit (forward signal side) and an amplifier 515 b, such asdifferential amplifier, for amplifying the terminal voltage of theresistor 515 a. The output side of the current detection circuit 515 isconnected to the control circuit 522 through the ac-dc conversioncircuit 516 and the amplifier 517. The output side of the resistor 515 ain the current detection circuit 15 is connected to the connectors 519a˜519 d through the switching circuit 518.

Further, the phase shift detection circuit 520, for example as shown inFIG. 45, is comprised by: a first flipflop (shortened to ff) circuit 520a 1; a second ff circuit 520 a 2; and an integration circuit 520 b forseparately inputting the forward signal from the oscillation circuit 511and the application signal to the antenna electrodes 504 (504 a˜504 d).

The passenger detection system having the above structure operates inthe following manner. First, the oscillation circuit 511 generates HFLVsignals whose voltage amplitude is detected by the detection section 514a of the amplitude detection circuit 514, and the detection signal isconverted to a dc signal in the ac-dc conversion circuit 514 b, and theamplified signal from the amplifier 514 c is input in the controlcircuit 522. The control circuit 522 judges whether the detected voltageamplitude meets the required amplitude value, and sends the amplifiedsignal to the amplitude varying section 513 a to correct the amplitudeto the required value. This process controls the voltage amplitude ofthe forward signal to a given voltage amplitude, and henceforth, voltageamplitude of the forward signal is corrected to a given amplitude valueby the coordinating action of the amplitude varying circuit 513 and theamplitude detection circuit 514.

The forward signal having a constant voltage amplitude is impressed onantenna electrodes 504 (504 a˜504 d) through the current detectioncircuit 515, switching circuit 518 (518 a˜518 d), connectors 519 a˜519d, resulting in the generation of weak electric fields in the vicinityof the antenna electrodes 504 (504 a˜504 d). In this process, switchingcircuits 518 are operated by signals from the control circuit 522 sothat, first, only the switching device 518 a is closed, next only theswitching device 518 b is closed, next only the switching circuit 518 cis closed, and such a stepwise successive switching is carried out sothat when a particular switch is being closed, other switches are allopened. Therefore, when a particular switching device 518 (518 a˜518 d)is closed, constant-amplitude forward signal passes through a particularswitching device 518 a˜518 d), a particular connector 519 (519 a˜519 d)and reaches a particular antenna electrode 504 (504 a˜504 d), generatingan electric field in the vicinity of a particular antenna electrode 504(504 a˜504 d), so that different values of the perturbation current,governed by the seating condition of the passenger, flow in the antennaecircuits. The perturbation current is detected by the current detectioncircuit 515, converted to de in the ac-dc conversion circuit 516,amplified in the amplifying circuit 517 and is successively input in thecontrol circuit 522. The sequence of switching may be in a reversedirection, such that 518 d, 518 c . . . to 518 a.

The signal (voltage) at both ends of the current detection circuit 15,that is, forward signal from the oscillation circuit 511 in theoscillation control circuitry and the rectangular application signal tothe antenna electrodes 504 (504 a˜504 d) in the switching circuitry(antenna electrode side) are input in the first and second ff circuits20 a 1, 20 a 2 of the phase shift detection circuit 520, and, as shownin Figure B, the leading edge (arrow) of the rectangle wave output fromthe forwarding side is detected at the terminal CK of the first ffcircuit 20 a 1, and the terminal bar outputs a “high”. In the meantime,in the receiving side also, as shown in Figure B, the leading edge(arrow) of the rectangle wave is detected at the terminal B of thesecond ff circuit 20 a 2, and the terminal bar Q puts out a one-shot lowsignal momentarily. When this output signal is input in the terminal RESof the first ff circuit 29 a 1, the output signal of the terminal bar Qof the first ff circuit 20 a 1 is inverted to a low, as shown in FigureC. This output represents the amount of phase shift (phasedifferential), and is converted to a voltage value by being integratedin the integration circuit 520 b, and is input in the control circuit522 through the amplifier 521. The phase shift detection is carried outsuccessively to correspond with the detection of forward current to eachantenna electrode by the current detection circuit 515.

In the control circuit 522, reference data are already stored such asthreshold values (threshold data) regarding the passenger seatingconditions (passenger loading, and identify adult/child), thresholdvalues regarding the phase difference between the forward signal to thecurrent detection circuit 515 and the application signal to the antennaelectrodes (threshold data). Specifically, passenger loading data areselected as follows. For example, as shown in FIGS. 48A, 48B, when anadult passenger P or a child passenger SP is seated on the seat 501, theareas opposing the individual antenna electrodes are different, and as aresult, the levels of the current flowing in the antenna electrodes aredifferent, such that when an adult passenger P is seated, the currentlevel is higher than that when a child passenger SP is seated.Therefore, a threshold value, which is somewhat lower than the currentlevel for a child passenger SP, is selected as the threshold value forpassenger loading. Thus, when detected data is higher than the thresholdvalue, it is assumed that a passenger is seated, and when it is lowerthan the threshold value, it is assumed that no one is seated. It ispreferable that the threshold value be selected according to a sum ofall the current flowing in each antenna electrode, but it is possible toselect a threshold value for each antenna electrode.

The identity of a passenger is determined as follows. As shown in FIGS.48A, 48B, when an adult passenger P or a child passenger SP is seated,the levels of the current flowing in individual antenna electrodes aredifferent depending on the contact area as explained above. Therefore,the threshold value for the identity of the passenger (whether thepassenger is an adult or a child) is selected as a current level midwaybetween the adult and child threshold values. Thus, when detected datais higher than the threshold value, it is assumed that a passenger isseated, and when it is lower than the threshold value, it is assumedthat a child SP is seated. It is preferable that the threshold value beselected according to a sum of all the current flowing in each antennaelectrode, but it is possible to select a threshold value for eachantenna electrode.

With respect to selecting a threshold value for the phase difference, asuitable value may be chosen between an average value of the phasedifference detected by the phase shift detection circuit 520 when aperson is present on the seat 501, and an average value of the phasedifference, caused by factors other than a human body. Thecharacteristics of the seat (wetness, for example) can affect themeasurements, therefore, upper and lower limits of threshold values arechosen, so that when the phase difference data are inside the range, itis assumed that a person is seated. Therefore, pre-stored data(regarding the passenger seating conditions and the phase difference)and the detected data (regarding the current levels and the phasedifference) are compared in the control circuit 22 to determine whethera seated passenger is an adult or a child, and what the characteristicsof the seat are.

Thus, signal data received by the control circuit 522 are comparedagainst the threshold data stored in the control circuit 522, so thatwhen the current levels in all the antenna electrodes 504 a˜504 d arehigh, it is assumed that seat 501 has a passenger and that the passengeris an adult P, as illustrated in FIG. 48A. In such a case, the controlcircuit 522 places the airbag apparatus 530 shown in FIG. 46 in thedeployable state. Conversely, when the current levels in all the antennaelectrodes 504 a˜504 d are low and are lower than the passenger loadingthreshold value, it is assumed that seat 501 has a passenger and thatthe person seated in a child SP, as illustrated in FIG. 48B. In such acase, the control circuit 522 places the airbag apparatus 530 shown inFIG. 46 in the not-deployable state. Specifically, when the airbag isnot to be activated, the control circuit 22 instructs the controlcircuit CC in the airbag apparatus 30 so that a gate signal is notsupplied to the switching element SW2 of the passenger side when acollision takes place. The driver-side switching element SW1 is suppliedwith a gate signal. When an adult and a child are seated, the switchingelements SW1, SW2 are both placed in the deployable state.

Next, the process of operation of the passenger detection system will beexplained with reference to the overall flowchart shown in FIG. 49.FIGS. 50˜53 show steps in sub-processes. First, as shown in FIG. 49, theignition circuit is turned on so that the process is in START. In stepS501, the program is initialized, and proceeds to step S502. In stepS502, initial diagnostics are performed for communication between thecontrol circuit 522 and the airbag apparatus 530. In step S503, itexamines whether the engine is operating, and if it is judged that theengine is operating, it proceeds to step S504. If it is judged that theengine is not operating, the program is shutoff. In step S504, signaldata related to the perturbation current flowing in a particular antennaelectrode and phase shift data related to passenger-seating conditions,resulting from the application of a weak electric field on theparticular antenna electrode of the antenna electrodes 504 a˜504 d, arereceived in the control circuit 522. In step S505, based on the receiveddata, passenger loading data, passenger identity data are examined andconclusions reached. In step S506, SRS process is carried out betweenthe control circuit 522 and the airbag apparatus (SRS) 530. When stepS506 is completed, it returns to step S504 and repeats the steps S504 toS506. Step S503 may be omitted.

Initial diagnostics are carried out as outlined in FIG. 50. First, instep SA501, stored data are sent from the control circuit 522 to thecontrol circuit CC in the airbag circuit 30. In step SA502, passengerdata are received from the airbag apparatus 530. In step SA503, it isexamined whether the received data from the airbag apparatus 530 matchthe stored data. If it is judged that the data are matched, the processis continued. If the data do not match, it is judged that problems existin the corn circuit and fail-safe process is carried out and alert lampis turned on, for example. The initial diagnostics may be carried out bysending the stored data from the airbag apparatus 530 to the controlcircuit 522 so that matching process can be carried out in the controlcircuit CC in the airbag apparatus 530.

Signal reception process is carried out as outlined in FIG. 51. First instep SB501, the control circuit 522 successively selects one switchingdevice at a time from the switching devices 518 a˜518 d so that only theswitching circuit 18 a and so on is closed, for example, to select anantenna electrode 504 a. In step SB502, the current data from therespective antenna electrode and phase difference are received in thecontrol circuit 522. In step SB503, it is examined whether successiveselection of antenna electrodes 504 a˜504 d by the successive actions ofthe switching devices 518 a˜518 d has been completed. If it is judgedthat the switching process has been completed, it proceeds to passengerevaluation process. If it is judged that the switching process isincomplete, it returns to step SB501.

The passenger evaluation process is carried out as outlined in FIG. 52.First, in step SC501, signal data related to the current levels flowingin all the antenna electrodes 504 a˜504 d and threshold values relatedto the passenger seating conditions are compared to decide whether themeasured signal data are higher than the threshold values. If themeasured signal data are higher than the threshold values, it proceedsto step SC502, and if it is judged that the signal data are not higher,it proceeds to step SC503. In step SC502, if it is judged that thepassenger sitting on the seat is an adult, it proceeds to step SC504, sothat ON-data for placing the airbag apparatus 530 in the deployablestate are entered in the SRS process, and the program connects to SRSprocess. Also, in step SC3, if the passenger sitting on the seat is achild, it proceeds to step SC505, and OFF-data for not deploying theairbag apparatus 530 are entered in the SRS process, and the program iscontinued.

The SRS process is carried out as outlined in FIG. 53. First, in stepSD501, ON-data for placing the airbag apparatus in the deployable stateor OFF-data for placing the airbag apparatus in the not-deployable stateand system check-data are sent from the passenger detection unitcircuitry (control circuit 22) to the airbag apparatus circuitry(control circuit CC). In step SD502, OK-data or NG-data in response tothe ON-data and OFF-data and system check-data from the airbag apparatuscircuitry are received by the control circuit 522, and it proceeds tostep SD503. In step SD503, it is judged whether the ON-/OFF-data andsystem check-data, sent from the passenger detection side to the airbagapparatus circuitry, are again returned from the airbag apparatuscircuitry to the passenger detection side in the normal condition. If itis judged to be normal (no problem in signal circuit), the process iscontinued. If there is a problem in the com circuit, it proceeds to stepSD504, and it is examined whether the fail-safe timer is at zero. Thisdetection process of circuit problems is programmed to repeat threetimes. Therefore, if it is judged that the fail-safe timer is zero,fail-safe process is carried out, and a warning lamp is activated, forexample. If it is judged that the fail-safe timer is not at zero, itproceeds to step SD505, and fail-safe timer count is performed, and theprocess is continued.

On the other hand, in step SE501, the airbag apparatus circuitry(control circuit CC) receives ON-data for placing the airbag apparatusin the deployable state or OFF-data for placing the airbag apparatus inthe not-deployable state and system check-data from the passengerdetection unit circuitry (control circuit 22). In step SE502, thereceived data are checked to examine whether or not they are normal. Ineither case, it proceeds to step SE503 for sending OK-data or NG-dataand system check-data to the passenger detection unit circuitry. If itis judged, in step SE502, that the signal circuit is normal, OK-data aresent in step SE503, and it proceeds to step SE504. In step SE504, thedata on the airbag side is renewed in response to the OK-data, therebyenabling to place the airbag in the deployable state or not-deployablestate. If, in step SE502, it is judged that there is a problem in thecom circuit, NG-data are sent to the control circuit 522 in step SE503,and it proceeds to step SE505. In step SE505, it is examined whether thefail-safe timer is at zero. This detection process of circuit problemsis programmed to repeat three times. Therefore, if it is judged that thefail-safe timer is zero, fail-safe process is carried out, and a warninglamp is activated, for example. If it is judged that the fail-safe timeris not at zero, it proceeds to step SE506, and fail-safe timer count isperformed, and the process is continued.

According to this embodiment, HFLV signals impressed on a plurality ofantenna electrodes 504 (504 a˜504 d) disposed on the seat 501 aregenerated by the oscillation circuit 511, but its output is obtained bythe trigger signals generated by triggering of a dc source (+Vcc) of apositive voltage (+5 volts for example) to switch the switching device511 b successively at a desired frequency (120 KHz for example),therefore, compared with a process of converting dc to high frequency acand waveforming the resulting signals, the circuit configuration of theoscillation circuit 511 as well as control circuit 510 can besimplified, enabling the system cost to be lowered.

Especially, by utilizing a single power source in the control unit 510,produced by the power circuit 524 for example +5 volts, and using thispower for the system power, the power circuit 524 as well as othercircuit configuration can be simplified even more, and system cost canbe significantly lowered.

Also, because the forward signal to the antenna electrodes 504 (504a˜504 d) is rectangular waveform of a substantially constant voltage,comparison/judging of stored data such as threshold values with thedetected data is simplified, and further, the output amplitude iscontrolled by the amplitude control circuit 512 so that reliability andaccuracy of judgment on passenger seating conditions by the controlcircuit 522 are even more improved.

Also, the control unit 510 is woven into the seat 501 having the antennaelectrodes 504, when connecting the antenna electrodes 504 to controlunit 510 using lead wires 506 (506 a˜506 d), the length of theconnecting wire can be shortened considerably compared with the case ofdisposing the control unit 510 on the dashboard or engine compartment.Therefore, system cost can be lowered and the effects of external noisecan be prevented, thereby improving the detection capability andreliability of the passenger detection system even more.

Because the control unit 510 is housed within the same housing as othercomponents such as the oscillation circuit 511, electric currentdetection circuit 515, switching circuit 518, control circuit 522, powercircuit 524, so that assembly into the seat 501 is facilitated.Especially, an installation space is readily available near the seatframe 503 or its vicinity, therefore, even if the size of the controlunit 510 becomes slightly larger, it can be simply and readilyaccommodated near the seat frame 503.

A plurality of antenna electrodes 504 (504 a˜504 d) are disposedseparately on the sitting section of seat 501, therefore, each antennaelectrode is successively connected to the oscillation circuit 511 bysuccessively switching the switching devices 518 a˜518 d in theswitching section 518, and by impressing HFLV to generate a weakelectric field, a particular value of current, determined by theopposing area of contact with the passenger and other factors, flows ineach antenna electrode 504. Therefore, by detecting the values of suchperturbation current, it is possible to detect readily whether thepassenger is an adult or a child.

Furthermore, the phase differential between the forward signals, fromthe oscillation circuits of the electric current detection circuit 515and the antenna electrode side, and the output signals to antennaelectrode 504 is dependent on the nature of the object sitting on theseat 501. Particularly, the levels of phase differential arerecognizably different when the object is a human body. Therefore, theuse of the phase shift detection circuit 520 to detect the phasedifference together with the result of passenger identity judgment basedon detected current levels, enables to reliably detect passenger loadingon the seat 501.

In particular, the airbag in the airbag apparatus 530 is able to be madeeither deployable or not deployable, depending on the judgment of thesystem on whether the passenger is an adult or a child. For example, ifit is judged that the passenger is a child based on a low-level ofdetected current, the airbag in the airbag apparatus 530 is placed in anon-deployable state. Therefore, even if the car collides, the airbag isnot opened and the child is prevented from suffering secondary injuries.

FIG. 54 shows another embodiment of the passenger detection system. Thissystem is basically the same as the system presented above, but thedifference is that the antenna electrodes 504 (504 a˜504 b) are providedon the backrest section 501 b, and they are not provided on the sittingsection 501 a.

As shown in FIG. 54A, when the opposing areas to all the antennaelectrodes 4 a˜4 d are wide, and the detected current levels are high,it is judged that the passenger sitting on the seat 501 is an adult.Also, as shown in FIG. 54B, when the opposing areas to all the antennaelectrodes 504 a˜504 d are small, and the detected current levels arelow, it is judged that the passenger sitting on the seat 1 is a child.

It should be noted that the present invention is not limited to theabove embodiment and other arrangements are possible. For example, thenumber of antenna electrodes (antenna electrode section) may be adjustedsuitably, and their shape can be rectangular or strip shape which arepossible examples. Electric field generation device may include an HFLVsource to produce substantially rectangle waveform by switching ofpositive electrical power source based on clock signals in the controlcircuit, or by dividing the clock signal in the control circuit. Theoutput frequency other than 120 KHz may be chosen depending on theconditions inside the car, and the voltage may be selected outside therange of 5 volts (3˜20 volts for example). Also, the amplitude controlcircuit and the phase shift detection circuit may be omitted dependingon the precision of the system power source and expected performancelevel of the system. Also, information detection circuit includes notonly the embodied example of direct detection of the antennae current,but includes such indirect detection circuits based on information onvoltages related to the perturbation current and waveform data. Further,passenger evaluation methods include comparison of stored data relatedto the seating pattern and sitting posture of the passenger withdetected data, thereby judging the passenger identity criteria such aspassenger loading, and whether the passenger is an adult or a child.

Embodiment 6

Next, the passenger detection system in Embodiment 6 will be presentedwith reference to FIGS. 55˜59. The passenger detection system in thisembodiment is based on detecting the perturbation current related to thepassenger seating conditions by processing the detected signals fromantenna electrodes using a common signal processing section. Those partswhich are the same as the parts shown in FIGS. 96˜97 will be given thesame reference numerals and their detailed explanations will be omitted.FIGS. 55˜57 show the arrangement of the passenger seat (driver seat) 601and the antenna electrodes, and seat 601 is comprised primarily of asitting section 601 a and a backrest section 601 b. The sitting section601 a is comprised by a seat frame 603 fixed to the base 602 which canbe moved forward and backward, and an outer covering for the cushion.Particularly, a plurality of antenna electrodes 604 (604 a˜604 d) ofsubstantially the same shape (for example, rectangle) are disposedsymmetrically on the sitting section 601 a. The antenna electrodesection 604 may be disposed on the outside the covering or on the outercovering or cushion material itself. A control unit 610 is assembledinto the seat 601, and is disposed on the seat frame 603 or itsvicinity.

The antenna electrode section 604 shown in FIG. 56 is basicallycomprised of a base member 605 made of an insulator such as non-wovenfabric, and antenna electrodes 604 a˜604 d placed separately andsymmetrically on one surface of the base member 605, and are placed onthe inside of the covering for the sitting section 601 a. The antennaelectrodes 604 a˜604 d are made of an electrically conductive fabric,but they made be made by: weaving fine metallic wire, or a conductivefiber into the base member 605 or into the seat cloth for the sittingsection 601 a, which may be regarded as the base member; or applying acoating using a conductive paint; or using a thin flexible metallicstrip. The antenna electrodes 604 a˜604 d to the base member 605 may beadhesively bonded or bonded using a thermoplastic or thermosettingmaterial, sewing, hooking, button, hooks, or adhesive tape, but adhesivebonding is preferred. The antenna electrodes 604 a˜604 d shown in thedrawing are formed into rectangles of substantially the same size. Theantenna electrode section 604 contain many antenna electrodes 604 a˜604d but they are essentially synonymous functionally and are usedinterchangeably in the following presentation.

The antenna electrode section 604 is constructed as shown in FIGS. 56A,56B. A lead wire 606 (606 a˜606 d) including shielding wire makes anelectrical/mechanical connection independently on one end of the antennaelectrodes 604 a˜604 d, using a connection terminal 607, and a terminallug 607A, and the lead wire 606 (606 a˜606 d) is attached to a connector609 at the output end, and is connected to the connectors (or terminals)613 a˜613 d of the control unit 610. Particularly, the connectionterminal 607 clamps antenna electrode with a metallic terminal toprovide electrical conduction, and brass rivets, hooks can be used.

In the above antenna electrode section 604, the connection structurebetween the antenna electrodes 604 a˜604 d and the lead wire 606 (606a˜606 d) are all essentially the same, therefore, explanation will bebased on connecting an antenna electrode 604 a to a lead wire 606 a. Theconnection terminal 607 is riveted through the antenna electrode 604 aand the base member 605. A connection terminal 607 is placed in the ahole provided through the antenna electrode 604 a and the base member605, and a riveting terminal lug 607A is inserted in the connectionterminal 607 prior to riveting, and when the assembly is riveted, itmakes an electrical connection between the terminal lug 607A and theantenna electrode 604 a through the connection terminal 607. Theterminal lug 607A is connected so as to make a mechanical/electricalcontact with the lead wire 606 a using a fastening means such aspressure lug 608.

The connection between the antenna electrode 604 a and the lead wire 606a may be made as shown in FIG. 56C and FIG. 57. In the former case, anextension member 604 aa is formed at a portion of the antenna electrode604 a, and the extension member 604 aa is connected to the connectionterminal 607. The latter case, one edge of the antenna electrode 604 ais folded to the back side of the base member 605, and the foldbacksection 604 ab, back side antenna electrode 604 a, base member 605 arejoined through a common hole by riveting a connection terminal 607.Also, terminal lug 607A is inserted in the connection terminal 607 priorto riveting.

The control unit 610 is assembled into the seat 601, and the controlunit 601 is comprised by, as shown in FIG. 58: an electric fieldgeneration device (forward current generation section) 611 forgenerating a weak electric field in the vicinity of the antennaelectrodes 604 a˜604 d; a switching circuit 612 connected to theforwarding line of the electric field generation device 611 and having aplurality of switching devices 612 a˜612 d for switching the antennaelectrodes 604 a˜604 d; connectors 613 a˜613 d disposed in the housingof the control unit, and connecting to the switching devices 612 a˜612 dof the switching circuit 518 during the switching action; an impedanceconversion circuit 614 connected to the forward line of the electricfield generation device 611 for receiving an ac voltage for applying tothe antenna electrode 604; an ac-dc conversion circuit 615 connected tothe impedance conversion circuit 614 for converting the output acsignals to direct current (smoothing circuit) 615; a control circuit 616including CPU, a/d conversion section, external memory (EEPROM, RAM forexample) and the like; a connector 617 connected to the battery source(not shown) disposed in the housing; and an electric power circuit 618connected to the connector 617. These components are contained in thesame housing for the control unit 610, which is fixed to the seat frame603 so as not to be exposed. An the airbag apparatus 630, shown in FIG.59 for example, is connected to the control circuit 616 in the controlunit 610. Selective switching of the switching devices 518 a˜518 d iscarried out according to the output signals from the control circuit616.

In this control unit 610, the electric field generation device 611 iscomprised by a series connected resistor 611 a and switching device 611b in a dc line of a positive constant dc voltage source Vcc, in thepower circuit 618, operated by the switching device (field-effect typetransistors) 611 b which is turned on/off by a gate signal from thecontrol circuit 616, so that HFLV signals of a rectangular waveform areoutput from the drain to the antenna electrodes through the signal lineand the switching circuit 612. The characteristics of HFLV signal aredetermined by the pulse-width-modulated (PWM) gate signal generated bythe control circuit 616, and is designed to output at substantially 120KHz. The duty ratio (ON-duty) of the gate signal is chosen at about 10%,but it may be changed depending on the circuit constant and operatingfrequency. The high frequency signal from the electric field generationdevice 611 to the switching circuit 612 is output when the switchingdevice (field effect transistor) 611 b is off, and its duty ratio isaround 90%.

In the control unit 610, the impedance conversion circuit 614 iscomprised by an op-amp having an amplification factor of 1, for example.Therefore, the output-side of the impedance conversion circuit 614 has alow impedance, and therefore, necessary current drain for operating CPUin the control circuit can be tolerated without affecting theperformance on the input-side. The ac-dc conversion circuit 615 isconnected to the output-side of the impedance conversion circuit 614,and is comprised by a smoothing circuit having a resistor 615 a and acondenser 615 b. The output-side of the ac-dc conversion circuit 615 isconnected to the control circuit 616.

In the control unit 610, the electric power circuit 618 is designed toproduces a singular power Vcc by adjusting the voltage form the batterypower (12 volts) to singular dc voltage at 5 volts using athree-terminal regulator to simplify the circuit. The constant voltageVcc produced by the power source circuit 618 is supplied to all theelements in the control unit 610 requiring the electrical power. It ispreferable that the Vcc source be the single voltage source but it ispossible to select other voltage values.

The passenger detection system having the above structure operates inthe following manner. First, the control circuit 616 periodicallyoperates the switching device 611 b by sending a gate signal shown inFIG. 60A. Whenever the gate signal becomes High, the switching device611 b is turned ON, and its drain is at the ground potential so thatthere is no output to the signal line. In this case, the current storedin stray capacitance around a particular selected antenna electrode isdischarged through the switching device 611 b. The method of selectionwill be described later. On the other hand, whenever the gate signalbecomes Low, the switching device 611 b is turned OFF, and an outputsignal of rectangular waveform HFLV signals (120 KHz, +5 volts) shown inFigure B are output to the signal line. The output signal is supplied tothe antenna electrode 604 (604 a˜694 d) through the signal line,switching circuit 612 (612 a˜612 d), connectors 613 a˜613 d, and as aresult, a weak electric field is generated in the vicinity of theantenna electrode 604 (604 a˜694 d). In this process, switching circuits612 are operated by signals from the control circuit 616 so that, first,only the switching device 612 a is closed, next only the switchingdevice 612 b is closed, and such a stepwise successive switching iscarried out so that when a particular switch is being closed, otherswitches are all opened. Therefore, when a particular switching device(612 a˜612 d) is closed, constant-amplitude forward signal passesthrough a particular a particular resistor 611 a, signal line, aparticular switching device (612 a˜612 d), a particular connector (613a˜613 d) and reaches a particular antenna electrode 604 (604 a˜604 d),thereby generating an electric field in the vicinity of a particularantenna electrode 604 (604 a˜604 d), so that different values ofperturbation current, governed by the seating condition of thepassenger, flow in the antennae circuits.

When the passenger seat 601 is vacant, perturbation current flows at alow level governed by the stray capacitance existing around theparticular antenna electrode. In this case, the rise time of the HFLVsignal is rounded, as shown in FIG. 60B, depending on the RC timeconstant governed by stray capacitance component and the resistor 611 a.On the other hand, when the passenger seat 601 is occupied, a largerstray capacitance is created in the vicinity of the particular antennaelectrode, compared with the vacant seat, and a high level current flowin the electrode. Because the capacitance component produced by an adultis larger than that produced by a child, the level of perturbationcurrent is higher. In this case, the rise time of the HFLV signal isexponential and is highly rounded by the influence of the RC timeconstant, as illustrated in FIG. 60C. The extent of rounding is affectedby the size of the capacitance component, and is higher for an adult andlesser for a child.

HFLV signals (voltage waveform) are processed in the impedanceconversion circuit (buffer circuit) 614 by the op-amp 614 a at anamplification factor of 1, such that it may exhibit various waveformsdepending on the RC time constant in the signal circuit including theelectric field generation device 611 and the antenna electrode circuitline. Thus, it is possible to obtain sufficient current for operatingthe control circuit 616 as necessary by making the input-side to be highimpedance and the output-side (ac-dc conversion circuitry) lowimpedance. Output HFLV signals from the impedance conversion circuit 614are input in the ac-dc conversion circuit 615. Here, ac signal isleveled by the resistor 615 a and the condenser 615 b in the smoothingcircuit, and is converted to a dc signal, as shown in FIG. 60D. In thedrawing, dotted line represents dc current level in a vacant condition,and the solid line represents the same in an occupied condition, and thetwo levels are clearly distinguishable. The dc conversion level isdependent on the value of the capacitance component existing around theantenna electrode for a given value of resistor 611 a in the RC timeconstant, so that it is high when an adult, which is a high capacitanceobject, is present while it is low when a child is present, and highestwhen the seat is vacant. The dc output current from the ac-dc conversioncircuit 615 is successively input in the control circuit 616, andprocessed by A/D conversion and stored in memory.

In the control circuit 616, reference data are already stored such asthreshold values (threshold data) regarding the seating conditions(detect passenger loading, and identify adult/child). Specifically,passenger loading data are selected as follows. For example, as shown inFIGS. 61A, 61B, when an adult passenger P or a child passenger SP isseated on the seat 601, the areas opposing the individual antennaelectrodes are different, and as a result, the capacitance componentsexisting in the vicinity of the antenna electrodes are different, suchthat when an adult passenger P is seated, not only the capacitance levelis higher than that when a child passenger SP is seated but the RC timeconstant is also affected such that the waveforms of the HFLV signalsare different, and the dc current levels output from the ac-dcconversion circuit 615 are different. Therefore, a threshold value fordetecting passenger loading is chosen to be a level midway between a dclevel caused by a child passenger and the vacant dc level shown bydotted line in FIG. 60D. Thus, when dc output data is lower than thethreshold value, it is assumed that a passenger is seated, and when itis higher than the threshold value, it is assumed that no one is seated.It is preferable that the threshold value be selected according to a sumof dc output from the ac-dc conversion circuit 615 representing all thecurrent flowing in each antenna electrode, but it is possible to selecta threshold value for each antenna electrode. The passenger identityprocess is omitted from this system.

Also, the threshold value regarding passenger identity is selected asfollows. For example, as shown in FIGS. 61A, 61B, when an adultpassenger P or a child passenger SP is seated on the seat 601, the areasopposing the individual antenna electrodes are different, and as aresult, the capacitance components existing in the vicinity of theantenna electrodes are different, such that when an adult passenger P isseated, not only the capacitance level is higher than that when a childpassenger SP is seated but the RC time constant is also affected suchthat the waveforms of the HFLV signals are different, and the dc currentlevels output from the ac-dc conversion circuit 615 are different.Therefore, a threshold value for detecting passenger loading is chosento be a level midway between a dc level caused by a child passenger andthe vacant dc level shown by dotted line in FIG. 60D. Thus, when the dcconversion data is lower than the threshold value, it is assumed that anadult P is seated, and when it is higher than the threshold value, it isassumed that a child SP is seated. It is preferable that the thresholdvalue be selected according to a sum of dc output from the ac-dcconversion circuit 615 representing all the current flowing in eachantenna electrode, but it is possible to select a threshold value foreach antenna electrode.

Thus, signal data received by the control circuit 616 are comparedagainst the threshold data stored in the control circuit 616, so thatwhen the dc output from the ac-dc conversion circuit 615 is low due tothe high current levels in all the antenna electrodes 604 a˜604 d and islower than the threshold value for passenger identity, it is assumedthat the passenger sitting on seat 601 is an adult P, as illustrated inFIG. 61A. In such a case, the control circuit 616 places the airbagapparatus 630 shown in FIG. 59 in the deployable state by the signalfrom the control circuit 616. Conversely, when the dc output from theac-dc conversion circuit 615 is high due to the low current levels inall the antenna electrodes 604 a˜604 d and is higher than the thresholdvalue for passenger identity, it is assumed that the passenger sittingon seat 601 is a child SP, as illustrated in FIG. 61B. In such a case,the control circuit 616 places the airbag apparatus 630 shown in FIG. 59in the not-deployable state by the signal from the control circuit 616.This results in the airbag in the airbag apparatus 630 becomes notdeployable by the signal from the control circuit 616. That is, when theairbag is to be deployed, the control circuit 616 sends a collisionsignal to the control circuit CC, and when the airbag is not to bedeployed, the gate current is not supplied to the element SW2 of thepassenger side when a collision takes place. The driver-side switchingelement SW1 is supplied with a gate signal. When the driver and an adultpassenger are seated, the switching elements SW1, SW2 are both placed inthe deployable state.

Next, the process of operation of the passenger detection system will beexplained with reference to the overall flowchart shown in FIG. 62.FIGS. 63˜66 show steps in sub-processes. First, as shown in FIG. 62, theignition circuit is turned ON so that the process is in START. In stepS601, the program is initialized, and proceeds to step S602. In stepS602, initial diagnostics are performed for communication between thecontrol circuit 616 and the airbag apparatus 630. In step S603, itexamines whether the engine is operating, and if it is judged that theengine is operating, it proceeds to step S604. If it is judged that theengine is not operating, the program is shutoff. In step S604, signaldata related to the perturbation current flowing in a particular antennaelectrode related to passenger seating conditions (ac-dc conversion),resulting from impressing a weak electric field on the particularantenna electrode of the antenna electrodes 604 a˜604 d, are received inthe control circuit 616. In step S605, based on the received data,passenger loading data, passenger identity data are examined andconclusions reached. In step S606, SRS process is carried out betweenthe control circuit 616 and the airbag apparatus (SRS) 630. When stepS606 is completed, it returns to step S604 and repeats the steps S604 toS606. Step S603 may be omitted.

Initial diagnostics are carried out as outlined in FIG. 63. First, instep SA601, stored data are sent from the control circuit 616 to thecontrol circuit CC in the airbag circuit 630. In step SA602, passengerdata are received from the airbag apparatus 630. In step SA603, it isexamined whether the received data from the airbag apparatus 630 matchthe stored data. If it is judged that the data are matched, the processis continued. If the data do not match, it is judged that problems existin the corn circuit and fail-safe process is carried out and alert lampis turned on, for example. The initial diagnostics may be carried out bysending the stored data from the airbag apparatus 630 to the controlcircuit 616 so that matching process can be carried out in the controlcircuit CC in the airbag apparatus 630.

Signal reception process is carried out as outlined in FIG. 64. First instep SB601, the control circuit 616 successively selects one switchingdevice at a time from the switching devices 612 a˜612 d so that only theswitching circuit 612 a and so on is closed, for example, to select anantenna electrode 604 a. In step SB602, the voltage data from therespective antenna electrode and ac-dc conversion data are received inthe control circuit 616 and stored. In step SB603, it is examinedwhether successive selection of antenna electrodes 604 a˜604 d by thesuccessive actions of the switching devices 612 a˜612 d has beencompleted. If it is judged that the switching process has beencompleted, it proceeds to passenger evaluation process. If it is judgedthat the switching process is incomplete, it returns to step SB601.

The passenger evaluation process is carried out as outlined in FIG. 65.First, in step SC601, the signal data on the perturbation currentflowing in the in all the antenna electrodes 604 a˜604 d related to thedc output current from the ac-dc conversion circuit 615 and thresholdvalues related to the passenger seating conditions are compared todecide whether the detected data are higher than the threshold values.If the detected data are smaller than the threshold values, it proceedsto step SC602, and if it is judged that the detected data are notsmaller, it proceeds to step SC603. In step SC602, if it is judged thatthe passenger sitting on the seat is an adult P, it proceeds to stepSC604, so that ON-data for placing the airbag apparatus 630 in thedeployable state are entered in the SRS process, and the programconnects to SRS process. Also, in step SC3, if the passenger sitting onthe seat is a child SP, it proceeds to step SC605, and OFF-data for notdeploying the airbag apparatus 630 are entered in the SRS process, andthe program is continued.

The SRS process is carried out as outlined in FIG. 66. First, in stepSD601, ON-data for placing the airbag apparatus in the deployable stateor OFF-data for placing the airbag apparatus in the not-deployable stateand system check-data are sent from the passenger detection unitcircuitry (control circuit 616) to the airbag apparatus circuitry(control circuit CC). In step SD602, OK-data or NG-data in response tothe ON-data and OFF-data and system check-data from the airbag apparatuscircuitry are received by the control circuit 616, and it proceeds tostep SD603. In step SD603, it is judged whether the ON-/OFF-data andsystem check-data, sent from the passenger detection side to the airbagapparatus circuitry, are again returned from the airbag apparatuscircuitry to the passenger detection side in the normal condition. If itis judged to be normal (no problem in signal circuit), the process iscontinued. If there is a problem in the com circuit, it proceeds to stepSD604, and it is examined whether the fail-safe timer is at zero. Thisdetection process of circuit problems is programmed to repeat threetimes. Therefore, if it is judged that the fail-safe timer is zero,fail-safe process is carried out, and a warning lamp is activated, forexample. If it is judged that the fail-safe timer is not at zero, itproceeds to step SD605, and fail-safe timer count is performed, and theprocess is continued.

On the other hand, in step SE601, the airbag apparatus circuitry(control circuit CC) receives ON-data for placing the airbag apparatusin the deployable state or OFF-data for placing the airbag apparatus inthe not-deployable state and system check-data from the passengerdetection unit circuitry (control circuit 616). In step SE602, thereceived data are checked to examine whether or not they are normal. Ineither case, it proceeds to step SE603 for sending OK-data or NG-dataand system check-data to the passenger detection unit circuitry. If itis judged, in step SE602, that the signal circuit is normal, OK-data aresent in step SE603, and it proceeds to step SE604. In step SE604, thedata on the airbag side is renewed in response to the OK-data, therebyenabling to place the airbag in the deployable state or not-deployablestate. If, in step SE602, it is judged that there is a problem in thecom 30 circuit, NG-data are sent to the control circuit 616 in stepSE603, and it proceeds to step SE605. In step SE605, it is examinedwhether the fail-safe timer is at zero. This detection process ofcircuit problems is programmed to repeat three times. Therefore, if itis judged that the fail-safe timer is zero, fail-safe process is carriedout, and a warning lamp is activated, for example. If it is judged thatthe fail-safe timer is not at zero, it proceeds to step SE606, andfail-safe timer count is performed, and the process is continued.

According to this embodiment, the ac-dc conversion circuit 615 isconnected, through the impedance conversion circuit 614, to the signalfor outputting HFLV signals generated by the electric field generationdevice 611. Therefore, passenger seating conditions are analyzed interms of the dc voltage signals (voltage waveforms) obtained by ac-dcconversion of the detected results related to the perturbation currentflowing on a plurality of antenna electrodes 604 (604 a˜604 d) disposedon the seat 601, thereby enabling to judge the passenger seatingconditions precisely.

Also, because of the presence of the impedance conversion circuit 614between the signal line and the ac-dc conversion circuit 615, theinput-side has a high impedance and the output-side has a low impedance.Therefore, when the control circuit 616 receives dc output from theac-dc conversion circuit 615, current drain by the control circuit 616does not affect the performance of the signal line. Therefore, passengerseating conditions can be detected with high precision.

Also, because the capacitance components in the vicinity of the antennaelectrodes are dependent on the passenger seating conditions on the seat601, RC time constant determined by resistor 611 a and capacitancecomponent may be chosen appropriately, the waveforms of HFLV signals inthe forwarding line are affected by the feedback effect of the passengerseating conditions. Therefore, the differences in the waveforms causedby differences in the rise time can be represented by ac-dc conversionusing the ac-dc conversion circuit 615, the detected data can bedistinguished, thereby providing information on passenger seatingconditions with precision.

Also, the passenger seating condition is judged from the output signalsfrom the ac-dc conversion circuit 615 and analyzed by the controlcircuit 616 in association with a plurality of antenna electrodes 604(604 a˜604 d), which are selected by the switching circuit 612.Therefore, the control circuit 616 bases its decision on a large amountof perturbation data, thereby improving the detection capability andreliability of the passenger detection system even more.

Also, the electric power circuit 618 as an element in the control unit610 produces a singular power source Vcc by reducing the voltage formthe battery power BA to singular dc voltage so that all the elements inthe control unit 610 requiring the electrical power will be served bythe same constant voltage Vcc, therefore, the electric circuit can beconstructed using a three-terminal regulator to simplify the circuit,and together with simplifying the structure of the antenna electrodesection, the system is simplified and the system cost is lowered.

Because the control unit 610 is housed within the same housing as othercomponents such as the electric field generation device 611, switchingcircuit 612, impedance conversion circuit 614, ac-dc conversion circuit615; control circuit 616; power circuit 524, so that assembly into theseat 601 is facilitated. Especially, an installation space is readilyavailable near the seat frame 603 or its vicinity, therefore, even ifthe size of the control unit 610 becomes slightly larger, it can besimply and readily accommodated near the frame 603.

A plurality of antenna electrodes 604 (604 a˜604 d) are successivelyimpressed with HFLV signals from the electric field generation device611, but the output is obtained by successively applying the gate signalto the switching device 611 b at a suitable frequency (such as 120 KHz)from a singular voltage source Vcc in the power circuit 618. Therefore,compared with oscillation circuit operated by dc-ac conversion and waveshaping, it is possible to produce a control circuit including theelectric field generation device 611 that is simple and cost effective.

Also, the control unit 610 is woven into the seat 601 having the antennaelectrodes 604, when connecting the antenna electrodes 604 to controlunit 610 using lead wires 606 (606 a˜606 d), the length of theconnecting wire can be shortened considerably compared with the case ofdisposing the control unit 610 on the dashboard or engine compartment.Therefore, system cost can be lowered and the effects of external noisecan be prevented, thereby improving the detection capability andreliability of the passenger detection system even more.

In particular, the airbag in the airbag apparatus 630 is able to be madeeither deployable or not deployable, depending on the judgment of thesystem on whether the passenger is an adult or a child. For example, ifit is judged that the passenger is a child based on a low-level ofdetected current, the airbag in the airbag apparatus 630 is placed in anon-deployable state. Therefore, even if the car collides, the airbag isnot opened and the child is prevented from suffering secondary injuries.

FIG. 67 shows another embodiment of the passenger detection system. Thecontrol unit 610A is basically the same as the control unit shown inFIG. 58, but the difference is that the electric field generation device611A is served by an oscillation circuit, and amplitude control circuit619 for maintaining the voltage amplitude substantially constant isconnected between the electric field generation device 611A and theswitching circuit 612. It is preferable that a resistor that forms anactive RC time constant be connected between the amplitude controlcircuit 619 and the junction of the impedance conversion circuit 614 tothe forwarding line.

The amplitude control circuit 619 is comprised by an amplitude varyingcircuit 620 for enabling to vary the voltage amplitude of the forwardsignal and amplitude detection circuit 621 for detecting the voltageamplitude of the forward signal. The amplitude varying circuit 620includes a variable amplitude section 620 a with programmable gainamplifier (PGA) and the amplitude detection circuit 621 includes: adetection section 621 a with an op-amp for detection of voltageamplitude; an ac-dc conversion circuit 621 b for converting the outputsignal from the detection section 621 a to dc; and an amplifier 621 cfor amplifying the output signal from the ac-dc conversion circuit 621b. Output signals from the amplifier 621 c are supplied to the controlcircuit 616, and variable amplitude signals for the variable amplitudesection 620 a are output from the contra circuit 616.

The amplitude control circuit 619 operates as follows. First, theoscillation circuit 611A generates HFLV signals, which are detected bythe detection section 621 a of the amplitude detection circuit 621, andthe detected signal is converted to a dc signal in the ac-dc conversioncircuit 621 b, amplified in the amplifier 621 c, and is input in thecontrol circuit 616. In the control circuit 616, detected amplitude ischecked whether it is at the required amplitude value, and variableamplitude signal is output to the variable amplitude section 620 a tocorrect to the required amplitude. Signal is corrected, and henceforth,the amplitude is retained at a constant level by the linked action ofthe amplitude varying circuit 620 and the amplitude detection circuit621. Forward signal having a constant amplitude is supplied to theantenna electrodes 604 (604 a˜604 d) through signal lines, switchingcircuit 612 (612 a˜612 d) and connectors 613 a˜613 d.

In this embodiment, voltage amplitude in the line voltage in the signallines (HFLV) is maintained constant so that stable dc can be output fromthe ac-dc conversion circuit 615, thereby improving the precision ofpassenger detection even more.

FIG. 68 shows another embodiment of the passenger detection system. Thecontrol unit 610B is basically the same as that shown in FIG. 58. Thedifferences are that one antenna electrode 604 is mounted on a sheet 601(sitting section 601 a or backrest section 601 b) is placed on thedashboard or in its vicinity, and the switching circuit 612 whichselectively switches or contact the electric field generation device 611and the antenna electrode 604 are omitted.

In this embodiment, because there is only one antenna electrode 604,data obtained from the ac-dc conversion circuit 615 are less, so thatthe passenger detection performance is slightly inferior, however, thecircuit configuration is simple and the system cost is lower.

Specially, if the antenna electrode 604 is placed on the dashboard ordoor or sideport of the seat, when it detects that a space between thepassenger and the dashboard or door becomes smaller than normal, becauseof the position of the passenger or other factors, the airbag apparatusor side airbag apparatus can be made not to deploy. This system can beapplied (use with) with the passenger detection system having aplurality of antenna electrodes shown in FIG. 58 or FIG. 67, it enablespassenger detection including passenger loading, identification as wellas sitting posture of the passenger.

FIG. 69 shows another embodiment of the passenger detection system. Thecontrol unit 610C is basically the same as that shown in FIG. 58. Thedifferences are that one particular antenna electrode among a pluralityof antenna electrodes 604 (604 a˜604 d) serves as signal forwardingantenna electrode by connecting to the electric field generation device611, and all other antenna electrodes can serve selectively as a signalreceiving antenna electrode by adding a switching circuit 612A.

In this embodiment, one particular antenna electrode among a pluralityof antenna electrodes 604 (604 a˜604 d) can be suitably combined withother antenna electrodes to serve as signal forwarding/receivingelectrode, and many such combinations are possible to increase the datavolume so that precision and reliability for passenger detection areincreased. Further, it is possible to carry out the function of theswitching circuit 612 shown in FIG. 58 by suitably controlling theswitching circuit 612A, and in such a system, data volume can beincreased even further.

FIG. 70 shows another embodiment of the passenger detection system. Thecontrol unit 610D is basically the same as that shown in FIG. 58. Thedifferences are: switching circuit 612 is disposed between the controlcircuit 616 and the electric field generation device 611; as manyelectric field generation device 611, impedance conversion circuits 614,and ac-dc conversion circuits 615 are provided as are antenna electrodes604 (604 a˜604 d); the signal line (output line) for the electric fieldgeneration device 611 is connected directly to the antenna electrodes604 a˜604 d through the connectors (terminals) 613 a˜613 d. In thediagram, connections of the power source Vcc to various components ofthe circuit are omitted. Also, although the control circuit 616 andswitching devices 612 a˜612 d in the switching circuit 612 are connectedby one signal line, but individual lines may be provided.

In this embodiment, in addition to obtaining the same benefits as thoseprovided by the system shown in FIG. 58, data from all the antennaelectrodes can be obtained concurrently in the control circuit 616 sothat the data volume is increased, and enables to detect grounding faultof any electrodes, for example, to improve precision and reliability ofpassenger sitting condition even more. For example, when an antennaelectrode that is being impressed with HFLV signals is touching anotherantenna electrode that is not being impressed with HFLV signals, dcsignals output from individual ac-dc conversion circuits 615 received inthe control circuit 616 would show different levels than normal, thusalerting possible touching of electrodes. Also, when a particularantenna electrode is grounded, dc signal output from the ac-dcconversion device 615 would be at an abnormal level.

Especially, this embodiment can be applied to the systems shown in FIGS.67, 69. For example, when applying to the system in FIG. 67, a switchingcircuit is provided between the electric field generation device 611Aand/he amplitude control circuit 612, and as many amplitude controlcircuits 619, impedance conversion circuit 614 and ac-dc conversioncircuit 615 are provided as there are antenna electrodes 604 (604 a˜604d).

FIG. 71 shows another embodiment of the passenger detection system,which is basically the same as those shown in FIGS. 55˜58. Difference isthat the backrest section of 601 b of the seat 601 is provided with aplurality of separate antenna electrodes 604 (604 a˜604 d) but thesitting section 601 b is not provided with any antenna electrode 604.

In this embodiment, as shown in FIG. 71A, when all the areas opposingthe antenna electrodes 604 a˜604 d are large, the capacitance componentsaround the antenna electrode become high, resulting in rounding of theline voltage waveform and decrease in the dc output level from the ac-dcconversion circuit 615, and, according to the threshold values, it isjudged that the passenger is an adult P. Also, as shown in FIG. 71B,when the opposing areas to individual antenna electrodes 604 a˜604 d aresmall, the capacitance components around the antenna electrode becomelow, resulting in less rounding of the line voltage waveform andincrease in the dc output level from the ac-dc conversion circuit 615,and, according to the threshold values, it is readily judged that thepassenger is a child SP.

It should be noted that the present invention is not limited to theabove embodiment and other arrangements are possible. For example, thenumber of antenna electrodes (antenna electrode section) may be adjustedsuitably, and their shape can be rectangular or strip shape which arepossible examples, and the antenna electrodes placed on the base membermay be covered with an insulating cover member. Electric fieldgeneration device may produce HFLV signals by appropriate switching ofclock signals in the control circuit, or by dividing the clock signal inthe control circuit. The output frequency other than 120 KHz may bechosen depending on the conditions inside the car, and the voltage maybe selected outside the range of 5 volts (3˜20 volts for example). Also,the impedance conversion circuit may be omitted depending on theexpected performance level of the system. Also, instead of the airbagapparatus, the control circuit may produce a warning light to indicatethe seat belt wearing condition. Further, passenger evaluation methodsinclude comparison of stored data related to the seating pattern andsitting posture of the passenger with the detected data, thereby judgingthe passenger seating condition including passenger loading, and whetherthe passenger is an adult or a child.

Embodiment 7

Next, some examples of the passenger detection system in Embodiment 7will be presented with reference to FIGS. 72˜74. This passengerdetection system is based on detecting the true perturbation currentrelated to passenger seating conditions by means of drift compensation.Accordingly, FIG. 72 shows a passenger (driver) seat, comprisedprimarily of a sitting section 701 a and a backrest section 701 b. Thesitting section 701 a includes a seat frame 703 fixed on a slidable base702 slidable forward or backward, a cushion member 704 disposed abovethe seat frame 703, an antenna electrode 705 disposed over the entiresurface of the sitting section 701 a, and the outer covering 706covering the antenna electrode 705. A control unit 710 is disposed on orin the vicinity of the seat frame 703.

The antenna electrode 705 is made of a conductive fabric in view ofpassenger comfort, but it may be made by weaving a metallic thread or aconductive fabric in the seat fabric or applying a conductive paint ordisposing flexible metal strips. The antenna electrode 705 is comprised(refer to FIG. 72C) by an antennae section 705 a covering almost theentire surface of the sitting section 701 a, a conduction section 705 bhaving a narrower width than the antennae section 705 a and extendingfrom a part of the antennae section 705 a, and connector 705 c providingthe electrical connection to the output end of the conductor section 705b. The conduction section 705 b is disposed so as to extend from thefront of the cushion member 704 to the seat frame 703, and the connectorat the output end is connected to the connector 712 of the control unit710.

As shown in FIG. 73, the control unit 710 is comprised by, an electricfield generation device (forward current generation section) 711 forgenerating weak electric field in the vicinity of the antenna electrode;a connector 712 connected to the signal line for forward signals outputfrom the electric field generation device 711; an impedance conversioncircuit 713 connected to the signal line for processing ac line voltagesto be applied to the antenna electrode 705; an ac-dc conversion circuit(smoothing circuit) 714 for receiving and converting ac output signals(line voltage) from the impedance conversion circuit 713 to a dcvoltage; a control circuit 715 including CPU, ac-dc conversion section,an external memory (for example, EEPROM, RAM); a connector 716 connectedto the battery source (not shown) disposed in the housing; and anelectric power circuit 717 connected to the connector 716. Thesecomponents are contained in the same housing for the control unit 710,which is fixed to the seat frame 703 so as not to be exposed. An theairbag apparatus 720, shown in FIG. 74 for example, is connected to thecontrol circuit 715 in the control unit 710.

Such an airbag apparatus 720 is comprised by: a driver-side squibcircuit comprised by a series circuit including safety sensor SS1, squibSQ1, and a solid-state switching device SW1 such as field effecttransistors; a passenger-side squib circuit comprised by a seriescircuit including safety sensor SS2, squib SQ2, and solid-stateswitching device SW2 such as field effect transistors; an electronicaccelerometer (impact sensor) GS; and a control circuit CC having afunction to judge an impact event on the basis of output signals fromthe sensor GS, and to supply signals to the gate circuits of switchingdevices SW1, SW2.

In the control unit 710, the electric field generation device 711 iscomprised by a series resistor 711 a and a switching device 711 b, in adc line of a positive constant dc voltage source Vcc in the powercircuit 717, operated by the switching device (field-effect typetransistors) 711 b which is turned ON/OFF by a gate signal from thecontrol circuit 715, so that HFLV signals of a rectangular waveform, areoutput from the drain to the antenna electrode 705 through the signalline and the connector 712. The characteristics of HFLV signal aredetermined by the pulse-width-modulated (PWM) gate signal output fromthe control circuit 715, and is designed to output at substantially 120KHz. The duty ratio (ON-duty) of the gate signal is chosen at about 10%,but it may be changed depending on the circuit constant and operatingfrequency. The HFLV signals are output from the electric fieldgeneration device 711 to the signal line when the switching device 711 bis off, and its duty ratio is about 90%.

In the control unit 710, the impedance conversion circuit 713 iscomprised by op-amp having an amplification factor of 1, for example.Therefore, the output-side of the impedance conversion circuit 713 has alow impedance, and therefore, necessary current drain for operating CPUin the control circuit may be tolerated without affecting theperformance on the input-side. The ac-dc conversion circuit 714 isconnected to the output-side of the impedance conversion circuit 713,and is comprised by a smoothing circuit having a resistor 714 a and acondenser 714 b. The output-side of the ac-dc conversion circuit 714 isconnected to the control circuit 715.

In the control unit 710, the electric power circuit 717 is designed toproduces a singular power Vcc by adjusting the voltage form the batterypower (12 volts) to singular dc voltage at 5 volts using athree-terminal regulator to simplify the circuit. The constant voltageVcc produced by the power circuit 717 is supplied to all the elements inthe control unit 710 requiring the electrical power. It is preferablethat the Vcc source be the single voltage source but it is possible toselect other voltage values.

The passenger detection system having the above structure operates inthe following manner. First, the control circuit 715 periodicallyoperates the switching device 711 b by sending a gate signal shown inFIG. 75A. Whenever the gate signal becomes High, the switching device711 b is turned ON, and its drain is at the ground potential so thatthere is no output to the signal line. In this case, the current storedin capacitance around the antenna electrode 705 is discharged throughthe switching device 711 b. On the other hand, whenever the gate signalbecomes Low, the switching device 611 b is turned OFF, and an outputsignal of rectangular waveform HFLV signals (120 KHz, +5 volts) shown inFigure B is output to the signal line. The output signal is impressed onthe antenna electrode 705 through the connector 712, and as a result, aweak electric field is generated in the vicinity of the antennaelectrode 705. The result is a flow of perturbation current of differentlevels dependent on seating conditions of the passenger.

When the passenger seat 701 is vacant, a perturbation current flows at alow level governed by the stray capacitance existing around the antennaelectrode 705. In this case, the rise time of the HFLV signal is roundedsomewhat, as shown in FIG. 75B, depending on the RC time constantgoverned by stray capacitance component and the resistor 711 a. On theother hand, when the passenger seat 701 is occupied, a larger straycapacitance is present in the vicinity of the antenna electrode 705,compared with the vacant seat, and a high level perturbation currentflow in the electrode 705. Because the capacitance component produced byan adult is larger than that produced by a child, the level ofperturbation current is higher. In this case, the rise time of the HFLVsignal is exponential and is highly rounded by the influence of the RCtime constant, as illustrated in FIG. 60C. The extent of rounding isaffected by the size of the capacitance component, and is higher for anadult and lesser for a child.

HFLV signals (voltage waveform) are processed in the impedanceconversion circuit (buffer circuit) 713 by the op-amp 714 a at anamplification factor of 1, such that it may exhibit various waveformsdepending on the RC time constant in the signal circuit including theelectric field generation device 711 and the antenna electrode circuitline. Thus it is possible to obtain sufficient current for operating thecontrol circuit 715 as necessary by making the input-side a highimpedance and the output-side (ac-dc conversion circuitry) a lowimpedance. HFLV signals output from the impedance conversion circuit 713are input in the ac-dc conversion circuit 714. Here, ac signal isleveled by the resistor 714 a and the condenser 714 b in the smoothingcircuit, and is converted to a dc signal, as shown in FIG. 75D. In thedrawing, dotted line represents dc current level in a vacant condition,and the solid line represents the same in an occupied condition, and thetwo levels are clearly distinguishable. The dc conversion level isdependent on the value of the capacitance component existing around theantenna electrode for a given value of resistor 711 a in the RC timeconstant, so that it is high when an adult, which is a high capacitanceobject, is present while it is low when a child is present. The dcoutput current from the ac-dc conversion circuit 714 is successivelyinput in the control circuit 715, and processed by A/D conversion andstored in memory.

In the control circuit 715, reference data are already stored such asthreshold values (threshold data) regarding the seating conditions(detect passenger loading, and identify adult/child). Specifically,passenger loading data are selected as follows. For example, as shown inFIGS. 76A, 76B, when an adult passenger P or a child passenger SP isseated on the seat 701, the areas opposing the individual antennaelectrodes are different, and as a result, the capacitance componentsexisting in the vicinity of the antenna electrodes are different, suchthat when an adult passenger P is seated, not only the capacitance levelis higher than that when a child passenger SP is seated but the RC timeconstant is also affected such that the waveforms of the HFLV signalsare different, and the dc current levels output from the ac-dcconversion circuit 714 are different. Therefore, a threshold value fordetecting passenger loading is chosen to be a level midway between a dclevel caused by a child passenger and the vacant dc level shown bydotted line in FIG. 75D. Thus, when de output data is lower than thisthreshold value, it is assumed that a passenger is seated, and when itis higher than the threshold value, it is assumed that no one is seated.

Also, the threshold value regarding the passenger identity is selectedas follows. For example, as shown in FIGS. 76A, 76B, when an adultpassenger P or a child passenger SP is seated on the seat 701, the areasopposing the antenna electrode are different, and as a result, thecapacitance components existing in the vicinity of the antenna electrodeare different, such that when an adult passenger P is seated, not onlythe capacitance level is higher than that when a child passenger SP isseated but the RC time constant is also affected such that the waveformsof the HFLV signals are different, and the dc current levels output fromthe ac-dc conversion circuit 714 are different. Therefore, a thresholdvalue for detecting the passenger loading is chosen to be a level midwaybetween the adult and child dc levels. Thus, when the dc conversion datais lower than the threshold value, it is assumed that an adult isseated, and when it is higher than the threshold value, it is assumedthat a child is seated.

Thus, signal data received by the control circuit 715 are comparedagainst the threshold data stored in the control circuit 715, so thatwhen the dc output from the ac-dc conversion circuit 615 is low due tothe high current level in the antenna electrode 705 and is lower thanthe threshold value for passenger identity, it is assumed that thepassenger sitting on seat 601 is an adult P, as illustrated in FIG. 76A.In such a case, the control circuit 616 places the airbag apparatus 720shown in FIG. 74 in the deployable state by the signal from the controlcircuit 715. Conversely, when the dc output from the ac-dc conversioncircuit 714 is high due to the low current level in the antennaelectrode 705 and is higher than the threshold value for passengeridentity, it is assumed that the passenger sitting on seat 701 is achild SP, as illustrated in FIG. 76B. In such a case, the controlcircuit 715 places the airbag apparatus 720 shown in FIG. 74 in thenot-deployable state by the signal from the control circuit 715. Thisresults in the airbag in the airbag apparatus 720 becomes not deployableby the signal from the control circuit 616.

When a collision occurs in this system, safety sensor SS1, SS2 areclosed responding to a relatively minor acceleration, and the squibcircuits on the driver-side and the passenger-side are placed in anoperable state. And, when the control circuit CC judges that a collisionhas definitely taken place according to the signals from theaccelerometer GS, signals corresponding to the judging results by thecontrol circuit 715 are sent to the gates of switches SW1, SW2. That is,when the result of judging by the control circuit 715 is an adult P, theswitches SW1, SW2 are turned ON, and when the result is a child, onlythe switch SW2 is turned OFF. These actions cause a current to flow inthe squib circuit, and owing to the heat generated by the respectivesquib SQ1 and SQ2 or SQ1, the airbags on the driver side and passengerside or only the passenger side airbag is turned ON, and the occupantsare protected from the impact.

The passenger detection system presented above is able to detectpassenger seating conditions precisely so as to enable appropriatecontrol of the airbag apparatus 720. Here, however, the properties ofthe components comprising the control unit 710, such as the electricfield generation device 711, impedance conversion circuit 713, ac-dcconversion circuit 714, may show a drift due to self-heating or changesin environmental temperature.

For example, resistors and condensers may change their resistance valueor charge capacity with rise in temperature, and switching elements suchas semiconductors also behave similarly. Therefore, the signal levelarising from the perturbation current in the antenna electrode 705 mayalso show a drift.

However, threshold data regarding the passenger seating conditionsstored in the control circuit 715 remain constant regardless oftemperature changes so that if the detected output level for the ac-dcconversion circuit 714 changes in the increasing direction, for example,and if it exceeds the threshold value, airbag may not be deployed uponcollision even when an adult passenger P is seated in the passenger seat701. Also, depending on the nature of the component material, if thedetected output signal level from the ac-dc conversion circuit 714changes in a decreasing direction and falls below the threshold value,the airbag may be deployed even when a child is seated in the passengerseat.

Therefore, it is necessary to ensure that regardless of temperaturechanges in the environment and changes in properties of components inthe control unit, the system must be able to assess the passengerseating conditions must be correctly.

The features of the system shown in FIG. 77 are as follows. Drift insignal output is corrected by the control circuit by correcting inputdata from an antennae interface circuit A that is associated with theantenna electrode 705 using data from a correction interface circuit Bthat is not associated with the antenna electrode 705. Interface circuitA and interface circuit B are configured in the same way, and while theantenna electrode 705 is connected to the electric field generationdevice 711 in interface circuit A, the antenna electrode 705 is notconnected to the electric field generation device 711 in interface B,and it is left as open circuit.

In this passenger detection system, control unit 710A is comprised by:antennae interface circuit A; correction interface circuit B; controlcircuit 715; and power circuit 717, and antennae interface circuit A isconnected to the antenna electrode 705 through the connector 712, andthe correction interface circuit B is not connected to the antennaelectrode 705, but is open circuited. The control unit 710A is connectedto the airbag apparatus 720.

In the control circuit 710A, as shown in FIG. 77B, interface circuit Aand interface circuit B are constructed in substantially the same way.These interface circuits include switching devices comprised by aresistor 711 a and a switching device such as FET device, and iscomprised by: an electric field generation device 711 operated by gatesignal from the control circuit 715; an impedance conversion circuit(buffer circuit) 713 connected to high frequency signal output line ofthe electric field generation device 711; and an ac-dc conversioncircuit 714 for converting output from the impedance conversion circuit713 to dc signal and leveling the signal using the smoothing circuitcomprised by resistor 714 a and a capacitor 714 b. The impedanceconversion circuit 713 includes an op-amp 713 a with an amplificationfactor of 1.

The operation of this system will be explained with reference to FIGS.77˜78. First, after turning the ignition switch, seat 701 is vacated. Inthis condition, gate signals such as the ones shown in FIG. 75A, areapplied to the switching devices 711 b of the electric field generationdevice 711 in the interface circuits A, B by the control circuit 715 sothat the electric field generation devices 711 output substantiallyrectangular shape HFLV signals (120 KHz, +5 volts). Output signal in theantennae interface circuit A is impressed on the antenna electrode 705through the signal line and connector 712, and a weak electric field isgenerated around the antenna electrode 705. As a result, a low levelcurrent flows caused by stray capacitance existing around the antennaelectrode 705, and the line voltage in the forward line of the electricfield generation device 711 exhibits a waveform showing FIG. 75B withslight rounding. On the other hand, because the forward line in thecorrection interface circuit B is open, line voltage in the electricfield generation device 711 exhibits a waveform with even less rounding.

Each line voltage is input in the ac-dc conversion circuits throughrespective impedance conversion circuits 713, and is converted torespective dc current. A low level signal Sin is output from the ac-dcconversion circuit 714 in the antennae interface circuit A as shown bythe dotted line in FIG. 78 and is received in the control circuit 715and stored in memory. On the other hand, a low level signal Hin that ishigher than Sin is output from the ac-dc conversion circuit 714 in thecorrection interface circuit B as shown by the solid line in FIG. 78 andis stored in memory. It is considered that, although Sin, Hin bothchange with time as a result of drifting, because both circuitconfigurations are the same, the same levels of drift are beingexperienced in both interface circuits A, B. Therefore, the differentialD₁ remains always constant. The difference D₁ is calculated as Hin−Sin.

Next, when a passenger is seated in seat 701, a larger capacitancecomponent is generated compared to the stray capacitance in the vacantstate, and a high level loaded current flows in the electrode 705.Therefore, there is large rounding effects on the waveform of theelectric field generation device 711 as shown in FIG. 75C. Therefore, alow level output signal Sin such as the one shown by the dotted envelopein FIG. 78 is output from the antennae interface circuit A. This outputsignal Sin is dependent on the passenger seating conditions. Thedifferential signal D₂ between the loaded state current signal andvacant state current signal Sin represents the amount of correction tobe applied to the vacant state output current signal Sin. Thedifferential D₂ is calculated according to a relation Hin−(Sin+D₁).

In the control circuit 715, threshold values of the differential D₂ isstored for the passenger seating conditions. For example, the thresholdvalue SH for passenger identity is related to the differential D₂ sothat when the differential D₂ is higher than the threshold value SH, thepassenger is judged to be an adult, and when the differential D₂ is lessthan the threshold value SH, the passenger is judged to be a child.

Therefore, the differential D₂ calculated according to the passengerseating conditions received in the control circuit 715 is compared withthe threshold values SH on the passenger seating conditions stored inthe control circuit 715. For example, as shown in FIG. 76A, when theopposing area to the antenna electrode 705 are large, and theperturbation current level is high, the dc output current from the ac-dcconversion circuit 714 is low, and the differential D₂ is large.Therefore, when the differential D₂ is higher than the threshold valueSH, the passenger seated in seat 701 is judged to be an adult. Theresult is that the airbag apparatus shown in FIG. 74 is placed, by theforward signal from the control circuit 715, in the deployable state.Conversely, as shown in FIG. 76B, when the opposing area to the antennaelectrode 705 are small, and the perturbation current level is low, thedc output current from the ac-dc conversion circuit 714 is high, and thedifferential D₂ is small. Therefore, when the differential D₂ is lowerthan the threshold value SH, the passenger seated in seat 701 is judgedto be a child SP. The result is that the airbag apparatus shown in FIG.74 is placed, by the forward signal from the control circuit 715, in thenot-deployable state.

When a collision occurs in this system, safety sensor SS1, SS2 areclosed responding to a relatively minor acceleration, and the squibcircuits on the driver-side and the passenger-side are placed in anoperable state. And, when the control circuit CC judges that a collisionhas definitely taken place according to the signals from theaccelerometer GS, signals corresponding to the judging results by thecontrol circuit 715 are sent to the gates of switches SW1, SW2. That is,when the result of judging by the control circuit 715 is an adult P, theswitches SW1, SW2 are turned ON, and when the result is a child, onlythe switch SW2 is turned OFF. These actions cause a current to flow inthe squib circuit, and owing to the heat generated by the respectivesquib SQ1 and SQ2 or SQ1, the airbags on the driver side and thepassenger side or only the driver side airbag is turned ON, and theoccupants are protected from the impact.

The process of operation of the passenger detection system will beexplained with reference to the overall flowchart shown in FIG. 79.FIGS. 80˜83 show steps in sub-processes. First, as shown in FIG. 79, theignition circuit is turned on so that the process is in START. In stepS701, the program is initialized, and proceeds to step S702. In stepS702, initial diagnostics are performed for communication between thecontrol circuit 715 and the airbag apparatus 720. In step S703, itexamines whether the engine is operating, and if it is judged that theengine is operating, it proceeds to step S704. If it is judged that theengine is not operating, the program is shutoff. In step S704, signaldata on ac-dc conversion for the antennae interface circuit A andcorrection interface circuit B are received in the control circuit 715.In step S705, based on the received data, data correction are performed,and passenger seating conditions are judged according to the correcteddata. In step S706, SRS process is carried out between the controlcircuit 715 and the airbag apparatus (SRS) 720. When step S706 iscompleted, it returns to step S704 and repeats the steps S704 to S706.Step S703 may be omitted.

Initial diagnostics in FIG. 79 are carried out as outlined in FIG. 80.First, in step SA701, stored data are sent from the control circuit 715to the control circuit CC in the airbag apparatus 720. In step SA702,passenger data are received from the airbag apparatus 720. In stepSA703, it is examined whether the received data from the airbagapparatus 720 match the stored data. If it is judged that the data arematched, the process is continued. If the data do not match, it isjudged that problems exist in the corn circuit and fail-safe process iscarried out and alert lamp is turned on, for example. The initialdiagnostics may be carried out by sending the stored data from theairbag apparatus 720 to the control circuit 715 so that matching processcan be carried out in the control circuit CC in the airbag apparatus720.

The passenger evaluation process is carried out as outlined in FIG. 81.First, in step SB701, in the vacant state, dc current signal Sin outputfrom the antennae interface circuit A (ac-dc conversion circuit 714 forimpressing current on the antenna electrode 705) is stored in memory inthe control circuit 715, and it proceeds to step SB702. In step SB702,in the vacant state, dc current signal Hin output from the antennaeinterface circuit B is stored in memory in the control circuit 715, andit proceeds to step SB703. In step SB703, differential D₁ (=Hin−Sin) iscalculated using signals Sin, Hin from interfaces A, B, respectively,retrieved from memory, and the result is stored in memory, and itproceeds to SB704. In step SB704, in measuring state, output signal Sinfrom the interface A is stored in memory. In step SB705, in measuringstate, output signal Hin from the interface B is stored in memory, andit proceeds to step SB706. In step SB706, differential D₂(=Hin−(Sin+D₁)) is calculated using signals Sin, Hin from interfaces A,B, respectively, retrieved from memory, and the result is stored inmemory, and it proceeds to SB707. In step SB707, passenger seatingconditions are judged based on differential D₂, and it returns to stepSB703.

The passenger evaluation process is carried out as outlined in FIG. 82.First, in step SC701, threshold values SH are compared with D₂ to decidewhether the measured D₂ is higher than the threshold values. If themeasured signal data are higher than the threshold values SH, itproceeds to step SC702, and if it is judged that the signal data are nothigher, it proceeds to step SC703. In step SC702, the passenger sittingon the seat is judged to be an adult, so that ON-data for placing theairbag apparatus 720 in the deployable state are entered in the SRSprocess. In step SC703, the passenger sitting on the seat is judged tobe a child, so that OFF-data for not deploying the airbag apparatus 720are entered in the SRS process.

The SRS process in FIG. 79 is carried out as outlined in FIG. 83. First,in step SD701, ON-data for placing the airbag apparatus in thedeployable state or OFF-data for placing the airbag apparatus in thenot-deployable state and system check-data are sent from the passengerdetection unit circuitry (control circuit 715) to the airbag apparatuscircuitry (control circuit CC). In step SD702, OK-data or NG-data inresponse to the ON-data and OFF-data and system check-data from theairbag apparatus are received by the control circuit 715, and itproceeds to step SD703. In step SD703, it is judged whether theON-/OFF-data and system check-data, sent from the passenger detectionside to the airbag apparatus circuitry, are again returned from theairbag apparatus circuitry to the passenger detection side in the normalcondition. If it is judged to be normal (no problems in com circuit),the process is continued. If there is a problem in the com circuit, itproceeds to step SD704, and it is examined whether the fail-safe timeris at zero. This detection process of circuit problems is programmed torepeat three times. Therefore, if it is judged that the fail-safe timeris zero, fail-safe process is carried out, and a warning lamp isactivated, for example. If it is judged that the fail-safe timer is notat zero, it proceeds to step SD5, and fail-safe timer count isperformed, and the process is continued.

On the other hand, in step SE701, the airbag apparatus circuitry(control circuit CC) receives ON-data for placing the airbag apparatusin the deployable state or OFF-data for placing the airbag apparatus inthe not-deployable state and system check-data from the passengerdetection unit circuitry (control circuit 715). In step SE702, thereceived data are checked to examine whether or not they are normal. Ineither case, it proceeds to step SE703 for sending OK-data or NG-dataand system check-data to the passenger detection unit circuitry. If itis judged, in step SE702, that the signal circuit is normal, OK-data aresent in step SE703, and it proceeds to step SE704. In step SE704, thedata on the airbag side is renewed in response to the OK-data, therebyenabling to place the airbag in the deployable state or not-deployablestate. If, in step SE702, it is judged that there is a problem in thecom circuit, NG-data are sent to the control circuit 22 in step SE703,and it proceeds to step SE705. In step SE705, it is examined whether thefail-safe timer is at zero. This detection process of circuit problemsis programmed to repeat three times. Therefore, if it is judged that thefail-safe timer is zero, fail-safe process is carried out, and a warninglamp is activated, for example. If it is judged that the fail-safe timeris not at zero, it proceeds to step SE706, and fail-safe timer count isperformed, and the process is continued.

In this system, an antennae interface circuit A and a correctioninterface circuit B of substantially the same circuit configuration areprovided in the control circuit 710, and the antenna electrode 705 isconnected to the electric field generation device 711 in the interfacecircuit A while the electric field generation device 711 in theinterface circuit B is not connected to the antenna electrode 705 andremain open circuited, therefore, the output signals Sin, Hin outputfrom the respective interface circuits A, B contain the same levels ofdrift contribution. Therefore, by computing the differential D₁ betweenthe output signals Sin, Hin, it is possible to eliminate the respectivedrift in each circuit.

In addition, it is possible to derive essentially true signal data D₂(=Hin−(Sin+D₁)) from the output signals Sin, Hin. Therefore, even is theoutput signals from the antennae interface circuit A are affected overtime by thermal effects, passenger seating conditions can always bedetermined according to correct information data. In other words, thesystem enables to avoid misdiagnose passenger seating conditions suchthat even though an adult is seated on seat 701, erroneous judgment ismade such that a child is seated on seat 701.

Also, in the interface circuit A, because the an ac-dc conversioncircuit 714 is connected to the signal line for outputting HFLV signalsfrom the electric field generation device 711 through the impedanceconversion circuit 713, the line voltage related to perturbation currentflowing in the antenna electrode 705 can be received through the signalline and converted to dc data, which is used to judge the passengerseating conditions.

Also, because the impedance conversion circuit 713 is connected betweenthe signal line and the ac-dc conversion circuit 714, the output-sidehas low impedance and the control circuit 714 can drain current from thedc output from the ac-dc conversion circuit 714 without affecting themeasurements in the signal line. Therefore, precision evaluation of thepassenger seating conditions can be performed.

Also, because the capacitance component existing around the antennaelectrode 705 is affected by the passenger seating conditions,therefore, by adjusting the RC time constant of the signal line circuit,it is possible to generate differences in rounding of the rise time ofthe HFLV signal to be impressed on the antenna electrode 705. Therefore,the difference in the output waveform from the antenna electrode 705 canbe converted to dc data in the ac-dc conversion circuit 714 to obtaindata to indicate the passenger seating conditions.

Also, HFLV signals to be impressed on the antenna electrode 705 areproduced by the electric field generation device 711 which is controlledby a singular power source Vcc, generated by switching the gate signalof the switching circuit 711 b, therefore, compared to the oscillationcircuit which performs waveform shaping after the conversion process,the circuit configuration is much simpler and more cost effective.

Further, the airbag in the airbag apparatus 720 is able to be madeeither deployable or not deployable, depending on the judgment of thesystem on whether the passenger is an adult or a child. For example, ifit is judged that the passenger is a child based on the level of dcoutput from the ac-dc conversion circuit 714, the airbag in the airbagapparatus 30 is placed in a non-deployable state. Therefore, even if thecar collides, the airbag is not opened and the child is prevented fromsuffering secondary injuries.

FIG. 84 shows another embodiment of the passenger detection system,which is basically the same as that shown in FIG. 77. Difference is thatthe antenna electrode 705A is disposed on the dashboard section DB.Here, the control unit is not shown but is disposed in the dashboardsection DB.

In this system, when the passenger P is too close to the dashboardsection DB (antenna electrode 705A), as illustrated by the dotted linein FIG. 84, perturbation current in the antenna electrode 705Aincreases, and the system detects that the passenger is too close andplaces the airbag in the not-deployable state. Drift in the detectedresults caused by thermal effects is negated by adopting a correctioninterface circuit so that the position of the passenger can be detectedprecisely at all times.

FIG. 85 shows another embodiment of the passenger detection system, andthe control unit 710 is basically the same as that in the system shownin FIG. 77. Differences are that a plurality of antenna electrodes aredisposed on the seat 701, a plurality of antennae interface circuitsA₁˜A_(n) and a switching circuit 715 having a plurality of switchingdevices 718 ₁˜718 n are disposed between these interface circuits andthe control circuit 715. The switching actions of the switching devices718 ₁˜718 _(n) in the switching circuit 718 are controlled by thesignals from the control circuit 715.

These interface circuits A₁˜A_(n) are constructed substantially in thesame way as the correction interface circuit B, and is comprised by theelectric field generation device 711, the impedance conversion circuit713 and the ac-dc conversion circuit 714. Individual antenna electrodesare connected to the interface circuits A₁˜A_(n) through the connectors712 ₁˜712 _(n), and the interface circuit B is not connected to theantenna electrode 705A but is open circuited.

In this system, because a plurality of antenna electrodes are disposedon the seat 701 and individual interface circuits A₁˜A_(n) are providedfor individual antenna electrodes in the control circuit B, the volumeof data output from the interface circuits A₁˜A_(n) is much increased sothat the passenger seating conditions can be assessed much moreprecisely. Here, regardless of the number of interface circuitsA₁˜A_(n), only one correction interface circuit B is needed, therebyavoiding congestion of circuits.

FIG. 86 shows another embodiment of the passenger detection system. Inthis system, the antennae interface circuit in the control unit 710C iscomprised by an antennae interface circuit AA and a correction interfacecircuit BB. The antenna electrode is connected is connected to theantennae interface circuit AA through the connector 712, and thecorrection interface BB is not connected to the antenna electrode, andis open circuited.

These interface circuits AA (BB) are comprised by: an electric fieldgeneration device 730; current detection circuit 731 for detecting thecurrent flowing in the signal line of the electric field generationdevice 730; an ac-dc conversion circuit 732 for converting the outputsignal from the current detection circuit 731 to dc; and an amplifierfor amplifying the output signal from the ac-dc conversion circuit 732.The electric field generation device 730 is the same as the device 711in FIG. 77, but it may be served by an oscillation circuit. Also, thecurrent detection circuit 731 includes a resistor 731 a for convertingcurrent to voltage and an amplifier 731 b for amplifying the voltagegenerated by the resistor 713 a. Here, output signals from theamplifiers 733 in interface circuits AA, BB are entered in the controlcircuit 715.

In this system, when the electric field generation device 730 impressesa current flow in the antenna electrode through the current detectioncircuit 731, a voltage is generated at the ends of the resistor 731 acorresponding to the current. This voltage is converted to a dc signalin the ac-dc conversion circuit 732, amplified in the amplifier 733 andis entered in the control circuit 715. In the meantime, output signalsfrom the interfaces AA, BB are also entered in the control circuit 715.In this case, however, the respective signals Sin, Hin are differentthan those shown in FIG. 77, 85, and the signal level of the outputsignal Sin from the interface AA is higher than the output signal Hinfrom the interface BB. Therefore, drift component D₁ is calculated asD₁=Sin−Hin and the true detected value D₂ of the perturbation current iscalculated as D₂=Sin−(Hin+D₁). Thus, the passenger seating conditionsare performed based on compensated measured signal data D₂ to provide anaccurate assessment.

It should be noted that the present invention is not limited by theembodiments presented above, and for example, the location of theantenna electrode may be on the door or near the seat, or on both endsof the dashboard. The antenna electrodes may be divided suitably andtheir shapes can be adjusted to other shapes such as strip shape. Whenmany antenna electrodes are to be used, it is preferable that they befirmly supported on an insulating base member. The electric fieldgeneration device can be produced by suitably dividing the clock signalsin the control circuit, and output frequency can be selected other than120 KHz to suit the condition inside the car, and the voltage can beselected to be other than 5 volt (3˜20 volt range). The impedanceconversion section 315Aa may be omitted depending on the detectioncontent and detection precision required by the system. Also, thejudging result of the control circuit can be applied to control of theseat belt use and warning light, for example. Further, passengerevaluation can be based on pre-stored reference data on seating patternof the passenger on the seat and sitting posture, and comparing thedetected data with the reference data to obtain information on passengerloading and passenger identity.

Embodiment 8

Embodiment 8 of the passenger detection system is based on detecting theperturbation current related to passenger seating condition using manyantenna electrodes processed by a single buffer circuit to preventsignal attenuation.

As shown in FIG. 87A, when two antenna electrodes E1, E2 are placedseparately, and an oscillation circuit 802 generating HFLV signals isconnected to one electrode E1, and the other electrode E2 is grounded,an electric field of characteristics governed by the difference in thepotential between the two electrodes E1, E2 is generated, and a currentI₂ flows in the antenna electrode E2. When an object OB is introduced inthe electric field, as shown in FIG. 87B, a perturbation current I₂′ ofa different characteristics than I₁ flows in the electrode E2.Therefore, the current flowing in the antenna electrode changesdepending on whether or not an object OB is seated on the seat. Theforegoing embodiments presented so far are all based on this principle.By increasing the number of antenna electrodes, it becomes possible toobtain a high volume of data on the object OB, including a passengersitting on the seat, to enable to detect passenger seating conditions.

Also, as shown in FIG. 88A, when HFLV signals are impressed on oneantenna electrode E3 from the oscillation circuit 802, a weak electricfield is generated around the antenna electrode E3, and a forwardcurrent I₃ flows in the circuit connected to the antenna electrode E3.When an object OB is introduced in the vicinity of the antenna electrodeE3, the existing weak electric field is disturbed, and, a perturbationcurrent I₃′ of different characteristics flows in the circuit of theantenna electrode E3. Therefore, detection of such forward currentenables to detect passenger seating conditions, and by increasing thenumber of antenna electrodes, much more information on the passenger maybe obtained. However, increasing the number of antenna electrodesintroduces complications including mutual signal interference effects.

Embodiment 8 is based on the principle illustrated in FIG. 88, theembodiments will be presented with reference to FIGS. 89˜91. Thepassenger seat 801 shown in FIG. 89 is comprised by a sitting section801 a and a backrest section 801 b, and a plurality of antennaelectrodes E1˜E4, a pair each electrode for example, provided on thesurfaces of the sitting section 801 a and the passenger seat 801 b. Theantenna electrodes E1, E2 are made of a conductive fabric in view ofpassenger comfort, but they may be made by weaving a metallic thread ora conductive fabric in the seat fabric or applying a conductive paint ordisposing flexible metal strips. These antenna electrodes E1˜E4 areconnected in the signal processing circuit 804 in the control unit 803shown in FIG. 90 by means of shield cables 805.

As shown in FIG. 91, the signal processing circuit 804 and its powersource (not shown) are housed in one housing of the control unit 803which may be fixed to a base 801 supporting the seat 801. The signalprocessing circuit 804 is comprised by: an oscillation circuit 806 forgenerating HFLV signals of 5˜12 volts at about 100 KHz; an amplitudecontrol circuit 807 for controlling the amplitude of the forward signalgenerated by the oscillation circuit 806 at a constant value; a currentdetection circuit 808 for detecting the forward current from theoscillation circuit 806; a switching circuit 809 for successivelyoperating the switching elements S1˜S4 between the current detectioncircuit 808 and each antenna electrode E1˜E4; and a control circuit 810including MPU for controlling the overall passenger detection system.Each antenna electrode E1˜E4 is connected to the current detectioncircuit 808 through respective switching element S1˜S4 by means of theshield cables 805. A shield cable 805 is comprised by a signal line 805m and a shield line 805 n for the signal line 805 m, and the ends of thesignal line 805 m connects antenna electrodes E1˜E4 to respectiveswitching elements S1˜S4, and shield line 805 n is grounded. Shieldcables 805 protects the forward/perturbation signals from the externalnoise to increase the precision of signal processing by the signalprocessing circuit 804.

The passenger detection System shown in FIG. 91 operates as follows.First, HFLV signals generated from the oscillation circuit 806 are sentto the amplitude control circuit 807 which controls the voltageamplitude constant, and the signal is sent to the current detectioncircuit 808. In the meantime, the control circuit 810 controls theon/off action of the switching circuit 809 so that, but only oneswitching element of the switching elements S1˜S4 is successively turnedon at any one time. For example, switching element S1 is turned on andall other switching elements are turned off. In so doing, HFLV signalsgenerated from the switching element S1 by the oscillation circuit 806,is impressed on only one antenna electrode E1, and a weak electric fieldis generated around the antenna electrode E1. Then, according to theprinciple illustrated in FIG. 88, forward current flows in the antennaelectrode E1, of characteristics governed by the conditions around theantenna electrode E1, and a perturbation current related to this currentflows in the current detection circuit 808, and is received (output) inthe control circuit 810 as the detected data (signal data) of thepassenger seating conditions. Next, only the switching element S2 isturned on, and a weak electric field is generated around the antennaelectrode E2, and forward current determined by the passenger seatingconditions is detected by the current detection circuit 808, and isreceived in the control circuit 810 as the detected data related to thepresent passenger seating conditions. Similarly, switching elements E3,E4 are successively turned on, and weak electric field generated aroundthe respective antenna electrode E3, E4 is generated, and forwardcurrent related to the passenger seating conditions is successivelyreceived in the control circuit 810 as the detected data.

In the control circuit 810, various signal data related to the sittingconditions in various sections of the seat 801 are computed to obtainpassenger seating pattern and other data regarding the detected sittingstate of the passenger. In the control circuit 810, various dataincluding reference sitting patterns are stored, and the detectedsitting pattern is computed from the detected data, which are comparedso as to extract a matching sitting pattern from the stored sittingpattern. The sitting patterns stored in the control circuit 810 includea vacant seat pattern (no passenger on the seat), adult normal pattern,back-facing child seat pattern (a child seat is facing backward),front-facing child seat pattern among others. When a detected sittingpattern is obtained in the control circuit 810, a corresponding signalis sent to the airbag apparatus (not shown), and instruction-data areentered in the CC circuit to instruct the airbag circuit to be either inthe deployable state or not-deployable state.

The passenger seating condition detection system presented above isbased on impressing HFLV signals on one antenna electrode to generateforward/perturbation current to be processed to obtain passenger seatingconditions, but a passenger detection system may also be based ontwo-electrode system illustrated in FIG. 87. In such a system, theantenna electrode circuit and the signal processing circuit areconnected using the shield cables which are used as both forward andreturn signal line for each antenna electrode.

Shield cables used to connect the antenna electrodes to the signalprocessing circuit reduces the external noise effects and improvesprocessing accuracy for detecting the passenger seating conditions.However, interference effects caused by the resistive and capacitivecomponents between the signal line and the shield line of the shieldcable sometimes affect the signal level adversely at both ends of theshield line (antenna electrode end and signal processing end). Suchsignal level errors occur more frequently when the cable lengthincreases. Non-uniform lengths of cables cause difficulty in correctingsuch errors. In actual application to automobiles, these difficultiesplaces serious limitations on distribution of antenna electrodes.Therefore, it is desirable to develop a passenger detection system thatis not affected by the lengths of the shield cables.

The following embodiments are designed to overcome such difficulties andwill be explained with reference to FIGS. 92˜95. These embodiments areapplications of the system shown in FIGS. 90 and 91, and those partswhich are the same as those in FIGS. 92˜95, 90, 91 are given the samereference numbers and their explanations are omitted.

As shown in FIG. 92, a buffer circuit 811 is inserted between a shieldline 805 n, connecting each of the antenna electrodes E1˜E4, and thesignal processing circuit 804, and the buffer circuits 811 are used toequalize the signal levels at the output ends of the signal line 805 mand the shield line 805 n. Buffer circuit 811 is comprised by an op-amp811′ such as in FIG. 93, and the positive terminal of the op-amp 811′(non-inverting input terminal) is connected to the signal line 805 m,and the negative terminal (inverting input terminal) is connected to theoutput terminal of the op-amp, and the output terminal of op-amp isconnected to the shield line 805 n.

When a buffer circuit 811 is connected between the signal line 805 m andthe shield line 805 n of one shield cable 805, the signal levels of theforward current flowing in the signal line 805 m or the return(perturbation) current are kept at the same level as the shield line 805n in the buffer circuit 811, therefore, there is no attenuation of thecurrent flowing in the signal line 805 m due to RC constant distributedcircuit formed between the signal line 805 m and the shield line 805.Therefore, errors in the signal levels at both ends of the signal line805 m are decreased. Therefore, when obtaining the passenger sittingdata according to the system designs shown in FIG. 87 or 88, regardlessof the length of the shield cable 805, precision data on passengerseating conditions can be obtained and processed in the signalprocessing circuit 804.

FIG. 94 shows a system based on the application of the present inventionon the passenger detection system shown in FIG. 91. A buffer circuit 811is inserted between the shield cables 805 and each of the switchingelements S1˜S4. The operation of the signal processing circuit 804 isthe same as that in FIG. 91. That is, HFLV signals are generated fromthe oscillation circuit 806 and are switched in the switching circuit809 by the successive on/off actions of the switching elements S1˜S4.

For example, only the switching element S1 is turned on and others areturned off, then, HFLV signals from the oscillation circuit 806 areimpressed only on the antenna electrode E1 through the signal line 805 mof one shield cable 805, which generates a weak electric field aroundthe antenna electrode E1, and a perturbation current related to theforward current flows in the antenna electrode E1, and the perturbationcurrent is detected by the current detection circuit 808 and is input inthe control circuit 810, as the present passenger sitting data.Attenuation in the signal line 805 m is reduced in the buffer circuit811, and the accuracy of the data detected by the current detectioncircuit 808 is improved, and high precision data are received in thecontrol circuit 810. Similarly, switches S2˜S4 are successively turnedon to obtain perturbation current related to the passenger seatingconditions on the antenna electrodes E2˜E4 are detected in the currentdetection circuit 808, and are received successively in the controlcircuit 810.

Next, the system shown in FIG. 95 will be explained. The system iscomprised by: a plurality of antenna electrodes E1˜En; shield cables805; a common buffer circuit 811. In this case, linking switchingelements S1′˜Sn′ which turns on/off as a unit with the switchingelements S1˜Sn in the switching circuits 809 are added to the switchingcircuit 809, and one buffer circuit 811 is connect to each shield line805 n of the shield cable 805 through the switching elements S1′˜Sn′. Inthis case, switching element S1 and its linking switching element S1′are turned on concurrently, and HFLV signals from the oscillationcircuit 806 are impressed only on antenna electrode E1 through thesignal line 805 m of one shield cable 805, and the perturbation currentrelated to the sitting conditions around antenna electrode E1 isdetected by the current detection circuit 808 and is output to thecontrol circuit 810. In this case, common buffer circuit 811 reduces theattenuation of the forward current flowing in the signal line 805 m, sothat the control circuit 810 receives high precision data as in thesystem shown in FIG. 94. Next, switching element S2 and the linkingswitching element S2′ are turned on concurrently, and the common buffercircuit 811 common to the shield cable 805 is connected to the switchingelement S2, and the forward current related to the passenger sittingcondition around the antenna electrode E2 is detected by the currentdetection circuit 808, and high precision data are received in thecontrol circuit 810. Similarly, switches S3˜Sn and the linking switchesS3′˜Sn′ are successively turned on to obtain perturbation signals fromthe antenna electrodes E3˜En, and are received successively in thecontrol circuit 810.

As shown in FIG. 95, by using a common buffer circuit for a plurality ofshield cables, cost is reduced, and in particular, circuit configurationcan be simplified significantly for a passenger detection system.

It should be noted that the present invention is not limited by theembodiments presented above. For example, the buffer circuit connectedbetween the signal processing section and the shield cables can beconnected to the electrode-end of the shield cable. Also, the buffercircuits are applicable to a passenger detection system based on theprinciple illustrated in FIG. 87.

1. A passenger detection method comprising the steps of: disposing aplurality of antenna electrodes separately on a seat; selecting aparticular antenna electrode from said plurality of antenna electrodes;generating a weak electric field on said particular antenna electrode;detecting information related to a current flowing in said particularantenna electrode resulting from applying said weak electric field; andjudging passenger seating conditions according to signal data related tosaid information.
 2. A passenger detection method comprising the stepsof: disposing a plurality of antenna electrodes separately on a seat;selecting a particular antenna electrode from said plurality of antennaelectrodes; generating a weak electric field on said particular antennaelectrode; detecting information related to a current flowing in saidparticular antenna electrode resulting from applying said particularweak electric field; evaluating passenger seating conditions accordingto signal data related to said information and producing a judgment;sending said judgment to an airbag apparatus so as to place an airbag ofsaid airbag apparatus either in the deployable state or not-deployablestate.
 3. A passenger detection system comprising: a plurality ofantenna electrodes disposed separately on a seat; an electric fieldgeneration device for generating a weak electric field around an antennaelectrode; an amplitude control circuit for maintaining an amplitude offorward signals substantially constant; a switching circuit forselecting a particular antenna electrode from said plurality of antennaelectrodes and providing an electrical connection to said electric fieldgeneration device; an information detection circuit for generating aparticular weak electric field around said particular antenna electrode,and obtaining information related to a current flowing in saidparticular antenna electrode resulting from applying said particularweak electric field; and a control circuit for receiving signal datafrom said information detection circuit and judging passenger seatingconditions on said seat according to said signal data.
 4. A passengerdetection system comprising: a plurality of antenna electrodes disposedseparately on a seat; an electric field generation device for generatinga weak electric field around an antenna electrode; an amplitude controlcircuit for maintaining an amplitude of forward signals substantiallyconstant; a switching circuit for selecting a particular antennaelectrode from said plurality of antenna electrodes and providing anelectrical connection to said electric field generation device; aninformation detection circuit for generating a particular weak electricfield around said particular antenna electrode, and obtaininginformation related to a current flowing in said particular antennaelectrode resulting from applying said particular weak electric field; acontrol circuit for receiving signal data from said informationdetection circuit and judging passenger seating conditions on said seataccording to said signal data; and an airbag apparatus for deploying,upon collision, an airbag designated for said seat; wherein said airbagapparatus is programmed by said control circuit to be either in thedeployable state or not-deployable state according to judging datagenerated by said control circuit.
 5. A passenger detection systemaccording to one of claim 3 or 4, wherein said plurality of antennaelectrodes are disposed on said sitting section and/or said backrestsection.
 6. A passenger detection system according to one of claim 3 or4, wherein said amplitude control circuit includes, at least, anamplitude varying circuit for varying a voltage amplitude of forwardsignals and an amplitude detection circuit for detecting said voltageamplitude and controlling said voltage varying circuit so as to maintainsaid voltage amplitude substantially constant, according to outputsignals from said amplitude detection circuit.
 7. A passenger detectionmethod comprising the steps of: disposing a plurality of antennaelectrodes separately on a seat; selecting a particular antennaelectrode from said plurality of antenna electrodes; generating a weakelectric field on said particular antenna electrode by impressing fieldsignals, whose voltage amplitude is controlled substantially constant,on said particular antenna electrode; detecting information related to acurrent flowing in said particular antenna electrode resulting fromapplying said particular weak electric field; and judging passengerseating conditions according to signal data related to said information.8. A passenger detection method comprising the steps of: disposing aplurality of antenna electrodes separately on a seat; selecting aparticular antenna electrode from said plurality of antenna electrodes;generating a weak electric field on said particular antenna electrode byimpressing field signals, whose voltage amplitude is controlledsubstantially constant, on said particular antenna electrode; detectinginformation related to a current flowing in said particular antennaelectrode resulting from applying said particular weak electric field;evaluating passenger seating conditions according to signal data relatedto said information and producing a judgment; and sending said judgmentto an airbag apparatus so as to place an airbag of said airbag apparatuseither in the deployable state or not-deployable state.
 9. A passengerdetection system comprising: a plurality of antenna electrodes disposedseparately on a seat; an electric field generation device for generatinga weak electric field around an antenna electrode; a switching circuitfor selecting a particular antenna electrode from said plurality ofantenna electrodes and providing an electrical connection to saidelectric field generation device; an information detection circuit forgenerating a particular weak electric field around said particularantenna electrode, and obtaining information related to a currentflowing in said particular antenna electrode resulting from applyingsaid particular weak electric field; and a control circuit for receivingsignal data from said information detection circuit and judgingpassenger seating conditions on said seat according to said signal data;wherein control circuit includes: memory means for storing initial dataSDn as reference data, obtained in a reference state including a vacantseat state by impressing a weak electric field on each antenna electrodeand detecting a resulting current flow in each antenna electrode;reception means for receiving detected data ADn, obtained when startingsaid passenger detection system by impressing a weak electric field oneach antenna electrode and detecting a resulting current flow in eachantenna electrode; and judging means for computing a difference betweensaid detected data ADn and said initial data SDn to produce essentiallydata DTn, where DTn=SDn−ADn, and judging passenger seating conditionsaccording to said essentially true data.
 10. A passenger detectionsystem comprising: a plurality of antenna electrodes disposed separatelyon a seat; an electric field generation device for generating a weakelectric field around an antenna electrode; a switching circuit forselecting a particular antenna electrode from said plurality of antennaelectrodes and providing an electrical connection to said electric fieldgeneration device; an information detection circuit for generating aparticular weak electric field around said particular antenna electrode,and obtaining information related to a current flowing in saidparticular antenna electrode resulting from applying said particularweak electric field; a control circuit for receiving signal data fromsaid information detection circuit and judging passenger seatingconditions on said seat according to said signal data; an airbagapparatus having a capability to select an operational state of anairbag designated for said seat; and communication means for sendingjudgment data, based on a judgment derived by said control circuit, tosaid airbag apparatus; wherein control circuit includes: memory meansfor storing initial data SDn as reference data, obtained in a referencestate including a vacant seat state by impressing a weak electric fieldon each antenna electrode and detecting a resulting current flow in eachantenna electrode; reception means for receiving detected data ADn,obtained when starting the passenger detection system, by impressing aweak electric field on each antenna electrode and detecting a resultingcurrent flow in each antenna electrode; and judging means for computinga difference between said detected data ADn and said initial data SDn toproduce essentially true data DTn, where DTn=SDn−ADn, and judgingpassenger seating conditions according to said essentially true data.11. A passenger detection method for a passenger detection system todetect seating conditions of a passenger seated on a seat by generatingan electric field successively in a plurality of antenna electrodesdisposed on said seat, detecting information related to a current flowin each antenna electrode caused by respective impressed electric fieldand judging passenger seating conditions according to said information,wherein said method includes the steps of: storing initial data SDn asreference data obtained in a reference state including a vacant seatstate, produced by impressing a weak electric field on each antennaelectrode and detecting a resulting current flow in each antennaelectrode; receiving detected data ADn, obtained after starting saidpassenger detection system, by impressing a weak electric field on eachantenna electrode and detecting a resulting current flow in each antennaelectrode; computing a difference between said detected data ADn andsaid initial data SDn to produce essentially true data DTn, whereDTn=SDn−ADn; and evaluating passenger seating conditions according tosaid essentially true data.
 12. A passenger detection method for apassenger detection system to detect seating condition of a passengerseated on a seat by generating a weak electric field around each of aplurality of antenna electrodes disposed on said seat, detectinginformation related to a current flow in each antenna electrode causedby respective impressed electric field, judging seating conditions basedon signal data related to said information, and sending said judgment toan air bag apparatus so as to place an airbag of said airbag apparatuseither in the deployable state or not-deployable state, wherein saidmethod includes the steps of: initializing sensors so as to storeinitial data SDn as reference data obtained in a reference stateincluding a vacant seat state, produced by impressing a weak electricfield on each antenna electrode and detecting a resulting current flowin each antenna electrode; and after starting said passenger detectionsystem, receiving detected data ADn, produced by successively impressinga weak electric field on each antenna electrode and detecting aresulting current flow in each antenna electrode; computing a differencebetween said detected data ADn and said initial data SDn to produceessentially true data DTn, where DTn=SDn−ADn; evaluating passengerseating conditions according to said true data; sending resultingevaluation data to airbag apparatus using communication means; and priorto placing said airbag apparatus in a selected operational state,performing an SRS process by exchanging evaluation data between apassenger detection circuitry and an airbag apparatus circuitry toexamine whether or not there is abnormality in communication circuitry.13. A passenger detection system having a plurality of antennaelectrodes disposed separately on a seat; an electric field generationdevice for generating a weak electric field around an antenna electrode;a switching circuit for selecting a particular antenna electrode fromsaid plurality of antenna electrodes and providing an electricalconnection to said electric field generation device; an informationdetection circuit for generating a particular weak electric field aroundsaid particular antenna electrode, and obtaining information related toa current flow resulting from said particular weak electric field; acontrol circuit for receiving signal data from said informationdetection circuit and judging passenger seating conditions on said seataccording to said signal data; an airbag apparatus for enabling todeploy, upon collision, an airbag designated for said seat; andcommunication means for sending a resulting judgment to said airbagapparatus, wherein resulting evaluation data are sent to airbagapparatus using communication means; and prior to placing said airbagapparatus either in the deployable state or not-deployable state,checking system operation by exchanging evaluation data between apassenger detection circuitry and an airbag apparatus circuitry toexamine whether or not there is abnormality in a communication circuitrybetween said passenger detection circuitry and said airbag apparatuscircuitry.
 14. A passenger detection method comprising the steps of:generating a weak electric field successively around a plurality ofantenna electrodes disposed on a seat; detecting information related toa current flowing in successive antenna electrodes; receiving signaldata regarding said information; evaluating passenger seating conditionsaccording to received signal data and producing a judgment; sending saidjudgment to an airbag apparatus; and prior to placing an airbag of saidairbag apparatus in a selected operational state; checking systemoperation by exchanging SRS data between a passenger detection circuitryand an airbag apparatus circuitry to examine whether or not there isabnormality in a communication circuitry between said passengerdetection circuitry and said airbag apparatus circuitry.
 15. A passengerdetection method for a passenger detection system to detect passengerseating conditions on a seat by generating a weak electric fieldsuccessively around a plurality of antenna electrodes disposed on aseat; detecting information related to a current flowing in successiveantenna electrodes; judging passenger seating conditions according tosignal data on said information; and sending a resulting judgment to anairbag apparatus so as to place an airbag designated for said seateither in the deployable state or not-deployable state, wherein whensaid seat is vacant, generating a weak electric field successively onsaid plurality of antenna electrodes; detecting information related to acurrent flowing in successive antenna electrode resulting from applyingsaid weak electric field; initializing sensors so as to store initialdata SDn obtained, in a reference state including a vacant seat state,by generating a weak electric field successively on a plurality ofantenna electrodes and detecting information related to a current flowcaused by respective weak electric field; and after starting saidpassenger detection system, receiving detected data ADn, produced bysuccessively impressing an electric field on each antenna electrode anddetecting a resulting current flow in each antenna electrode; computinga difference between said detected data ADn and said initial data SDn toproduce essentially true data DTn, where DTn=SDn−ADn; evaluatingpassenger seating conditions according to said essentially true data;sending resulting evaluation data to airbag apparatus usingcommunication means; and prior to placing said airbag apparatus in aselected operational state, performing an SRS process by exchangingevaluation data between a passenger detection circuitry and an airbagapparatus circuitry to examine whether or not there is abnormality in acommunication circuitry between said passenger detection circuitry andsaid airbag apparatus circuitry.
 16. A passenger detection systemaccording to one of claims 14 or 15, wherein a problem diagnostic stepis added to an overall method of passenger detection.
 17. A passengerdetection system comprising: a plurality of antenna electrodes disposedseparately on a sitting section and/or a backrest section of a seat; anelectric field generation device for generating a weak electric fieldaround an antenna electrode; a current detection circuit for applyingsaid weak electric field to a particular antenna electrode and detectinga resulting current flowing in said particular antenna electrode; and acontrol circuit for evaluating passenger sitting conditions according tosignal data received from said current detection circuit; wherein allantenna electrodes, excepting said particular antenna electrode selectedfor generating a weak electric field, are impressed with a directcurrent potential or earth potential.
 18. A passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on asitting section and/or a backrest section of a seat; an electric fieldgeneration device for generating a weak electric field around an antennaelectrode; a switching circuit having a plurality of switching devicesfor selecting a particular electrode and connecting said electric fieldgeneration device to said particular antenna electrode; a currentdetection circuit for applying said weak electric field to saidparticular antenna electrode and detecting a resulting current flowingin said particular antenna electrode; and a control circuit forevaluating passenger sitting conditions according to signal datareceived from said current detection circuit; wherein all antennaelectrodes, excepting said particular antenna electrode selected forgenerating a weak electric field, are impressed with a direct currentpotential or earth potential.
 19. A passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on asitting section and/or a backrest section of a seat; an electric fieldgeneration device for generating a weak electric field around an antennaelectrode; a current detection circuit for applying said weak electricfield to a particular antenna electrode and detecting a resultingcurrent flowing in said particular antenna electrode; and a controlcircuit for evaluating passenger sitting conditions according to signaldata received from said current detection circuit; wherein all antennaelectrodes, excepting said particular antenna electrode selected forgenerating a weak electric field, are impressed with a direct currentpotential or earth potential, and evaluation data from said controlcircuit are sent to an airbag apparatus so as to place an airbagdesignated for said seat in the deployable state or not-deployablestate.
 20. A passenger detection method by generating a weak electricfield selectively around a particular antenna electrode selected from aplurality of antenna electrodes disposed separately on a sitting sectionand/or backrest section of a seat; applying a direct current potentialor earth potential to all antenna electrodes excepting said particularantenna electrode; and evaluating passenger seating conditions accordingto signal data of a perturbation current resulting from applying saidweak electric field.
 21. A passenger detection method by generating aweak electric field selectively around a particular antenna electrodeselected from a plurality of antenna electrodes disposed separately on asitting section and/or backrest section of a seat; applying a directcurrent potential or earth potential to all antenna electrodes exceptingsaid particular antenna electrode; and evaluating passenger seatingconditions according to signal data of a perturbation current resultingfrom applying said weak electric field to produce an evaluation result,and sending instruction data based on said evaluation result from saidcontrol circuit to an airbag apparatus so as to place an airbagdesignated for said seat in the deployable state or not-deployablestate.
 22. A passenger detection system comprising: a plurality ofantenna electrodes disposed separately on a seat; an electric fieldgeneration device for generating a weak electric field around an antennaelectrode; a switching circuit for selecting a particular electrode andconnecting said electric field generation device to said particularantenna electrode; an information detection circuit for applying saidweak electric field to said particular antenna electrode and detectinginformation related to a current flowing in said particular antennaelectrode resulting from applying said weak electric field; and acontrol circuit for evaluating passenger sitting conditions according tosignal data received from said information detection circuit; whereinsaid electric field generation device outputs high frequency low voltagesignals having a rectangular waveform.
 23. A passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on aseat; an electric field generation device for generating a weak electricfield around an antenna electrode by outputting high frequency lowvoltage signals having a rectangular waveform; a switching circuit forselecting a particular electrode and connecting said electric fieldgeneration device to said particular antenna electrode; an informationdetection circuit for applying said weak electric field to saidparticular antenna electrode and detecting information related to acurrent flowing in said particular antenna electrode resulting fromapplying said weak electric field; and a control circuit for evaluatingpassenger sitting conditions according to signal data received from saidinformation detection circuit to produce an evaluation result, andsending instruction data based on said evaluation result from saidcontrol circuit to an airbag apparatus so as to place an airbagdesignated for said seat in the deployable state or not-deployablestate.
 24. A passenger detection system according to claim 22 or 23,wherein a plurality of antenna electrodes are disposed on a sittingsection and/or a backrest section of a seat.
 25. A passenger detectionsystem according to claim 22 or 23, wherein electric field generationdevice generates high frequency low voltage signals of a rectangularwaveform by switching a direct current voltage maintained at a positiveconstant voltage at a selected frequency.
 26. A passenger detectionsystem according to claim 22 or 23, wherein electric field generationdevice generates high frequency low voltage signals of a rectangularwaveform by dividing a clock signal in a control circuit at a selectedinterval.
 27. A passenger detection method by generating a weak electricfield selectively around a particular antenna electrode selected from aplurality of antenna electrodes disposed separately on a seat; applyinghigh frequency low voltage signals of a rectangular waveform on saidparticular antenna electrode; and detecting information related toperturbation current flowing is said particular antenna electrode; andevaluating passenger seating conditions according to signal data relatedto said information.
 28. A passenger detection method by generating aweak electric field selectively around a particular antenna electrodeselected from a plurality of antenna electrodes disposed separately on aseat; applying high frequency low voltage signals of a rectangularwaveform on said particular antenna electrode; and detecting informationrelated to a perturbation current flowing is said particular antennaelectrode; and evaluating passenger seating conditions according tosignal data related to said information to produce an evaluation result,and sending instruction data based on said evaluation result from saidcontrol circuit to an airbag apparatus so as to place an airbagdesignated for said seat in the deployable state or not-deployablestate.
 29. A passenger detection system comprising: an antenna electrodedisposed on a sitting section and/or a backrest section of a seat; anelectric field generation device for generating a weak electric fieldaround said antenna electrode; an ac-dc conversion circuit forconverting an alternating current line voltage in a forward line,related to a perturbation current flowing in said antenna electroderesulting from said weak electric field generated around said antennaelectrode produced by connecting said antenna electrode to said electricfield generation device, to a direct current voltage; and a controlcircuit for judging passenger seating conditions according to evaluationdata output from said conversion circuit.
 30. A passenger detectionsystem comprising: a plurality of antenna electrodes disposed separatelyon a sitting section and/or a backrest section of a seat; an electricfield generation device for generating a weak electric field around anantenna electrode; a switching circuit for selecting a particularelectrode and connecting said electric field generation device to saidparticular antenna electrode; an ac-dc conversion circuit for applyingsaid weak electric field to said particular antenna electrode, andconvening a resulting alternating current line voltage in a forward linerelated to a perturbation current flowing in said particular electrodeto a direct current voltage; and a control circuit for judging passengerseating conditions according to signal data output from said conversioncircuit.
 31. A passenger detection system comprising: a plurality ofantenna electrodes disposed separately on a sitting section and/or abackrest section of a seat; an electric field generation device forgenerating a weak electric field around an antenna electrode; aswitching circuit for selecting a particular electrode to serve as asending electrode and selecting a pairing electrode serving a receivingelectrode, and connecting said electric field generation device to saidparticular antenna electrode; an ac-dc conversion circuit for generatinga weak electric field between a resulting pair of antenna electrodes,and converting a resulting alternating current line voltage in a forwardline related to a perturbation current flowing in said particularelectrode to a direct current voltage; and a control circuit for judgingpassenger seating conditions according to signal data output from saidconversion circuit.
 32. A passenger detection system comprising: aplurality of antenna electrodes disposed separately on a sitting sectionand/or a backrest section of a seat; an electric field generation devicefor generating a weak electric field around an antenna electrode; aswitching circuit for selecting a particular electrode and connectingsaid electric field generation device to said particular antennaelectrode; an ac-dc conversion circuit for applying said weak electricfield to said particular antenna electrode, and converting a resultingalternating current line voltage in a forward line related to aperturbation current flowing in said particular electrode to a directcurrent voltage; and a control circuit for judging passenger seatingconditions according to signal data output from said conversion circuitto produce an evaluation result, and sending instruction data based onsaid evaluation result from said control circuit to an airbag apparatusso as to place an airbag designated for said seat in the deployablestate or not-deployable state.
 33. A passenger detection systemcomprising: a plurality of antenna electrodes disposed separately on asitting section and/or a backrest section of a seat; an electric fieldgeneration device for generating a weak electric field around an antennaelectrode; a switching circuit for selecting a particular electrode andconnecting said electric field generation device to said particularantenna electrode; an ac-dc conversion circuit for applying said weakelectric field to said particular antenna electrode, and converting aresulting alternating current line voltage in a forward line related toa perturbation current flowing in said particular electrode to a directcurrent voltage; and a control circuit for judging passenger seatingconditions according to signal data output from said conversion circuit.34. A passenger detection system comprising: a plurality of antennaelectrodes disposed separately on a sitting section and/or a backrestsection of a seat; an electric field generation device for generating aweak electric field around an antenna electrode; a switching circuit forselecting a particular electrode and connecting said electric fieldgeneration device to said particular antenna electrode: an ac-dcconversion circuit for applying said weak electric field to saidparticular antenna electrode, and converting a resulting alternatingcurrent line voltage in a forward line related to a perturbation currentflowing in said particular electrode to a direct current voltage; and acontrol circuit for judging passenger seating conditions according tosignal data output from said conversion circuit to produce an evaluationresult, and sending instruction data based on said evaluation resultfrom said control circuit to an airbag apparatus so as to place anairbag designated for said seat in the deployable state ornot-deployable state.
 35. A passenger detection system according to oneof claims 29 to 34, wherein an RC time constant circuit is formed bycapacitance components existing in a vicinity of an antenna electrodeand a resistor connected in series to a forward circuitry including anelectric field generation device.
 36. A passenger detection systemaccording to one of claims 29 to 34, wherein an impedance conversioncircuit is provided between a forward circuitry for sending outputsignals from an electric field generation device and an ac-dc conversiondevice.
 37. A passenger detection system according to claim 36, whereinsaid impedance conversion circuit is comprised by an operationalamplifier having an amplification factor of
 1. 38. A passenger detectionsystem according to one of claims 29 to 34, wherein said control circuitis comprised, at least, by memory means for storing threshold valuerelated to passenger seating conditions, means for receiving outputsignals from an ac-dc conversion circuit, and a judging section forjudging passenger seating conditions by comparing threshold values withreceived signal data.
 39. A passenger detection system according to oneof claims 29 to 34, wherein said electric field generation device, saidac-dc conversion circuit, and said control circuit are housed in acommon housing to form a control unit, which is incorporated in saidseat.
 40. A passenger detection system according to one of claims 29 to34, wherein said electric field generation device, ac-dc conversioncircuit, and said control circuit are housed in a common housing to forma control unit, and those constituting elements requiring an electricpower source are supplied with power from an electric power source Vccoutputting a constant direct current voltage.
 41. A passenger detectionsystem comprising: an antenna electrode disposed on a sitting sectionand/or a backrest section of a seat; an electric field generation devicefor generating a weak electric field around said antenna electrode; anantennae interface circuit including a detection circuit for detectinginformation related to a perturbation current flowing in said antennaelectrode resulting from applying a power from said electric fieldgeneration device; a correction interface circuit including a detectioncircuit for detecting information related to a perturbation currentflowing in said antenna electrode resulting from applying a power fromsaid electric field generation device; and a control circuit forcorrecting signals output from said antennae interface circuit accordingto signal data output from said antennae interface circuit and saidcorrection interface circuit; wherein said antennae interface circuitand said correction interface circuit are configured similarly and saidantennae interface circuit is connected to an antenna electrode and saidcorrection interface circuit is not connected to an antenna electrodeand is open-circuited.
 42. A passenger detection system comprising: anantenna electrode disposed on a sitting section and/or a backrestsection of a seat; an electric field generation device for generating aweak electric field around an antenna electrode; an antennae interfacecircuit including a detection circuit for detecting information relatedto a perturbation current flowing in an antenna electrode resulting fromapplying a power from said electric field generation device; acorrection interface circuit including a detection circuit for detectinginformation related to a perturbation current flowing in an antennaelectrode resulting from applying a power from said electric fieldgeneration device; a control circuit for correcting signals output fromsaid antennae interface circuit according to signal data output fromsaid antennae interface circuit and said correction interface circuit;and an airbag apparatus that can be placed in a specific operationalstate according to judgment data generated by said control circuit;wherein said antennae interface circuit and said correction interfacecircuit are configured similarly and said antennae interface circuit isconnected to an antenna electrode and said correction interface circuitis not connected to an antenna electrode and is open-circuited.
 43. Apassenger detection system according to one of claim 41 or 42, whereinsaid antennae interface circuit is comprised of, at least: an electricfield generation device for generating a weak electric field around anantenna electrode; an ac-dc conversion circuit for connecting an antennaelectrode to said electric field generation device to generate a weakelectric field, and converting ac voltage related to a perturbationcurrent flowing in said antenna electrode, resulting from applying saidweak electric field, to dc data.
 44. A passenger detection systemaccording to claim 43, wherein an RC time constant circuit is formed bycapacitance components existing in a vicinity of an antenna electrodeand a resistor connected in series to a forward circuitry including anelectric field generation device.
 45. A passenger detection systemaccording to claim 43, wherein an impedance conversion circuit isprovided between a forward circuitry for sending output signals from anelectric field generation device and an ac-dc conversion device.
 46. Apassenger detection system according to claim 45, wherein said impedanceconversion circuit is comprised by an operational amplifier having anamplification factor of
 1. 47. A passenger detection system according toone of claim 41 or 42, wherein said control circuit is comprised of, atleast: memory means for storing signal data output from said correctioninterface circuit; means for receiving signals output from said antennaeinterface circuit; a correction section for compensating for driftaccording to correction data received; an evaluation section forevaluating passenger seating conditions according to correction resultsoutput from said correction section.
 48. A passenger detection systemaccording to one of claim 41 or 42, wherein said antennae interfacecircuit and said correction interface circuit are comprised by, atleast: an electric field generation device; a current detection devicefor detecting a perturbation current produced by application of power bysaid electric field generation device; wherein said antennae interfacecircuit is connected to an electrode and said correction circuit is notconnected to an antenna electrode and is open-circuited.
 49. A passengerdetection system comprised by antenna electrodes disposed on a seatinside an automobile connected, using a shielding cable whose signalline is shielded by a shielding line, to a signal processing circuit fordetecting passenger seating conditions by processing signal data relatedto a perturbation current flowing in an antenna electrode resulting fromapplying a weak electric field generated about said antenna electrode,wherein a buffer circuit, for maintaining signal levels of signal lineand shield line at a same level, is connected between said signal lineand said shield line.
 50. A passenger detection system according toclaim 49, wherein a plurality of antenna electrodes are disposed on saidseat, and antenna electrodes and said signal processing circuit arewired using a plurality of shielding cables.
 51. A passenger detectionsystem according to claim 49, wherein a common buffer circuit isconnected to each of said plurality of antenna electrodes and signalprocessing circuit through a respective switching element.